Undercutting system for use in conjunction with sacroiliac fusion

ABSTRACT

A method and apparatus for preparing a region between adjacent bones for fusion. A first aperture is formed that extends through one of the bones. An undercutting system is inserted into the first aperture. The undercutting system includes an insertion apparatus and a cutting assembly. A first path is cut between the adjacent bones by extending or retracting the cutting assembly with respect to the insertion apparatus.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/865,592, filed Jan. 9, 2018, which is a divisional of U.S. patentapplication Ser. No. 14/593,579, filed Jan. 9, 2015, now U.S. Pat. No.9,861,375, issued Jan. 9, 2018, which claims the benefit of U.S.Provisional Application Number No. 61/925,280, filed Jan. 9, 2014. Eachof the foregoing applications are hereby incorporated by reference intheir entirety for continuity of disclosure.

FIELD OF THE INVENTION

An embodiment of the invention is directed to a method for treatingpatients experiencing sacroiliac joint pain. More particularly, theinvention relates to a system for preparing a space between the sacrumand the iliac to facilitate sacroiliac joint fusion.

BACKGROUND OF THE INVENTION

The sacroiliac joint is located at the intersection of the ilium, theupper bone of the pelvis, and the sacrum at the base of the spine. Oneof the primary functions of the sacroiliac joint is to provide shockabsorption of pressures put on the spine.

Certain persons experience pain in the sacroiliac joint. This pain mayresult from a variety of causes, examples of which include injuries,incorrect vertebra fusion during pre-birth development and effects ofpregnancy.

If initial efforts to reduce the pain in the sacroiliac joint throughphysical therapy and/or steroid injections are not effective, surgerymay be needed to fuse together the sacroiliac joint. One typicalsurgical technique involves forming an incision in the lower back overthe sacroiliac joint. The articular cartilage is removed from bothsurfaces. This process is also called chondrectomy.

The sacrum and the ilium are held together with screws or a plate.Eventually, bone grows between the sacrum and the ilium to thereby fusetogether the sacroiliac joint. Because of the challenges in accessingthe surfaces of the sacrum and the ilium that will fuse together, thistype of surgery may result in damage to tissue, nerves and/or bloodvessels that surround the sacroiliac joint. Such damage may prevent thepatient from fully realizing the benefits of the sacroiliac joint fusionand in some instances cause the patient to experience more pain afterthe sacroiliac joint fusion than before the sacroiliac joint fusion.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed to an undercutting system forpreparing a region between an ilium and a sacrum for sacroiliac fusion.The undercutting system includes an insertion apparatus and a cuttingassembly.

The cutting assembly is operably mounted with respect to the insertionapparatus. The cutting assembly has a distal end and a proximal end. Thecutting assembly includes a plurality of cutting elements and a cuttingelement attachment mechanism.

The cutting element attachment mechanism engages the cutting elements tooperably mount the cutting elements with respect to the insertionapparatus. The cutting element attachment mechanism permits the cuttingelements to pivot with respect to each other.

Another embodiment of the invention is directed to an undercuttingsystem for preparing a region between an ilium and a sacrum forsacroiliac fusion. The undercutting system includes an insertionapparatus and a cutting assembly. The cutting assembly is operablymounted with respect to the insertion apparatus.

The cutting assembly has a distal end and a proximal end. The cuttingassembly includes an elongated base and a plurality of cutting elements.The elongated base is fabricated from a flexible material. The pluralityof cutting elements is movable with respect to the elongated base. Thecutting elements are configured to cut on at least one of moving towardsthe distal end or the proximal end of the cutting assembly.

Another embodiment of the invention is directed to an undercuttingsystem for preparing a region between an ilium and a sacrum forsacroiliac fusion. The undercutting system includes an insertionapparatus and a cutting assembly. The cutting assembly is movable withrespect to the insertion apparatus between a retracted configuration andan extended configuration. In the extended configuration at least aportion of the cutting assembly extends from the insertion apparatus.The cutting assembly has a plurality of kerfs formed therein. The kerfsare oriented at an angle with respect to an upper surface of the cuttingassembly.

Another embodiment of the invention is directed to a method of preparinga region between adjacent bones for fusion. A first aperture is formedin one of the bones. Wherein the at least one aperture extends throughone of the bones. An undercutting system is inserted into the firstaperture. The undercutting system includes an insertion apparatus and acutting assembly. A first path is cut between the adjacent bones byextending or retracting the cutting assembly with respect to theinsertion apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 is a side view of an undercutting system for use in a sacroiliacfusion procedure.

FIG. 2 is a bottom view of the undercutting system of FIG. 1.

FIG. 3 is a sectional view of the undercutting system taken along a line3-3 in FIG. 2.

FIG. 4 is a side view of a control mechanism for use in the undercuttingsystem of FIG. 1.

FIG. 5 is a top view of the control mechanism of FIG. 4.

FIG. 6 is a top view of a cutting assembly for use in the undercuttingsystem of FIG. 1.

FIG. 7 is a side view of the cutting assembly of FIG. 6.

FIG. 8 is a top view of an alternative configuration of the cuttingassembly.

FIG. 9 is a side view of the cutting assembly of FIG. 8.

FIG. 10 is a partially cut away perspective view of an aperture beingdrilled in the sacrum and the ilium as an initial step in a sacroiliacfusion procedure.

FIG. 11 is a partially cut away perspective view of an undercuttingsystem being inserted into the aperture.

FIG. 12 is a partially cut away perspective view of the undercuttingsystem being used to form an undercut region between the sacrum and theilium.

FIG. 13 is a partially cut away perspective view of fasteners insertedinto the apertures.

FIG. 14 is an exploded perspective view of an alternative configurationof the cutting assembly.

FIG. 15 is a partially assembled perspective view of the cuttingassembly of FIG. 14.

FIG. 16 is an assembled perspective view of the cutting assembly of FIG.14.

FIG. 17 is a sectional view of the cutting assembly of FIG. 14 extendingfrom an insertion apparatus.

FIG. 18 is a top view of the cutting assembly of FIG. 14 used to form aplurality of grooves in a cutting process.

FIG. 19 is a perspective view of an alternative embodiment of theundercutting system in an insertion configuration.

FIG. 20 is a perspective view of the undercutting system of FIG. 19 in aretraction configuration.

FIG. 21 is a side view of the cutting assembly from the undercuttingsystem of FIG. 19 where the cutting assembly is in the insertionconfiguration.

FIG. 22 is a side view of the cutting assembly from the undercuttingsystem of FIG. 19 where the cutting assembly is in the retractionconfiguration.

FIG. 23 is a top view of the undercutting system of FIG. 19 used to forma plurality of paths between an ilium and a sacrum in a patient.

FIG. 24 is a side view of a power device used in conjunction with theinsertion apparatus to cause extension and retraction of the probeassembly and/or the cutting assembly.

FIG. 25 is a side view of an alternative embodiment of a distal end ofthe insertion apparatus.

FIG. 26 is a front view of an alternative embodiment of a distal end ofthe insertion apparatus.

FIG. 27 is a sectional view of the insertion apparatus taken along aline C-C in FIG. 26.

FIG. 28 is a front view of an alternative embodiment of a distal end ofthe insertion apparatus.

FIG. 29 is a sectional view of the insertion apparatus taken along aline C-C in FIG. 28.

FIG. 30 is a perspective view of an alternative embodiment of thecutting assembly in a retracted configuration.

FIG. 31 is a perspective view of the cutting assembly of FIG. 30 in afirst partially expanded configuration.

FIG. 32 is a perspective view of the cutting assembly of FIG. 30 in asecond partially expanded configuration.

FIG. 33 is a perspective view of the cutting assembly of FIG. 30 in afully expanded configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is directed to an undercutting system 10,such as is illustrated in FIGS. 1-3. The undercutting system 10 may beused for preparing surfaces of the ilium 14 and the sacrum 16 forsacroiliac joint fusion, which are illustrated in FIG. 10. Theundercutting system utilizes an aperture 20 formed in the ilium 14 toaccess a region 22 between the ilium 14 and the sacrum 16.

A person of skill in the art will appreciate that the undercuttingsystem 10 may be used in other surgical applications where it is desiredto remove tissue between two bones that are located in close proximityto each other especially where it is not possible or desirable todirectly access the tissue between the two bones utilizing a lateralapproach.

In certain embodiments, the aperture 20 may have a diameter of up toabout 50 millimeters. In other embodiments, the aperture 20 may have adiameter of between about 6 millimeters and 15 millimeters.

The undercutting system 10 thereby enables tissue such as cartilage tobe removed from the adjacent surfaces of the ilium 14 and the sacrum 16and for at least a portion of the adjacent surfaces of the ilium 14 andthe sacrum 16 to be removed or otherwise disturbed. This procedure maybe referred to as preparing bleeding bone surfaces on the ilium 14 andthe sacrum 16, which are more receptive to growing bone between them aspart of sacroiliac joint fusion.

Thereafter, the ilium 14 and the sacrum 16 may be held in a stationaryposition with respect to each other such as with a screw that isextended through the aperture 20, as is discussed in more detail below.Maintaining the ilium 14 and the sacrum 16 in the stationary positionfacilitates bone growth between the ilium 14 and the sacrum 16 tothereby fuse the sacroiliac joint.

Performing the sacroiliac fusion using the undercutting system 10disclosed herein reduces the complexity of the sacroiliac fusion whencompared to prior techniques used for sacroiliac fusion and thereby hasthe potential to decrease the patient recovery time from the sacroiliacfusion procedure.

Additionally, sacroiliac fusion performed using the concepts describedherein has the potential of fewer side effects because this process doesnot require the surgeon to work proximate the nerves and/or bloodvessels, as is done with prior sacroiliac fusion techniques.

Furthermore, the apparatus and technique disclosed herein do notformally expose the sacroiliac joint during the process of preparing thesacroiliac joint for fusion and thereby reduces the potential ofinfection. The time associated with preparing the surfaces of the iliumand the sacrum is also reduced when compared to the prior more invasivetechniques used to prepare the sacroiliac joint for fusion.

The undercutting system 10 may include an insertion apparatus 30 and aprobe assembly 32 that extends from a distal end of the insertionapparatus 30, as illustrated in FIGS. 1-3. The insertion apparatus 30may include an elongated shaft 40 that is formed with a length thatenables a proximal end thereof to be positioned outside of the patient'sbody while a distal end thereof is utilized to the prepare the regionbetween the ilium 14 and the sacrum 16 for the sacroiliac fusionprocess. In certain embodiments, the length of the elongated shaft 40 isbetween about 15 centimeters and about 45 centimeters.

The probe assembly 32 may have a relatively flat configuration and beformed from a flexible and strong material that resists breakage. Anexample of one such material is nitinol. A beneficial quality of nitinolis that nitinol is bendable but returns to the unbent configuration whenthe force that caused the bending is removed, even at high strains. Theprobe assembly 32 is intended to pass through the tissue between theilium 14 and the sacrum 16 and thereby define a path through the tissuefor the subsequent cutting operation.

As such, the probe assembly 32 should be sufficiently sharp to cutthrough the tissue between the ilium 14 and the sacrum 16 while notbeing sharp enough such that the probe assembly 32 has a tendency to cutinto the ilium 14 or the sacrum 16. The edges of the probe assembly 32may be sharp enough to cut through this tissue without any additionalsharpening.

A distal end of the probe assembly 32 may be curved but not sharpened tofacilitate the probe assembly 32 being extended from the insertionapparatus 30 to define a path through the tissue but without cuttinginto the ilium 14 and the sacrum 16 during the extension process.

The probe assembly 32 may include more than one layer. Utilizingmultiple layers enables the probe assembly 32 to exhibit enhancedflexibility when compared to a single layer configuration. In amulti-layer configuration, one of the layers may be thicker. This layerwould be viewed as the primary and the other layer(s) would be viewed asthe auxiliary layer(s).

In certain embodiments, the main layer may have a thickness that isbetween about 30% and about 60% greater than the thickness of theauxiliary layer(s). In other embodiments, the main layer may have athickness that is about 50% thicker than the thickness of the auxiliarylayer(s).

The main layer may have a thickness of between about 0.010 inches andabout 0.030 inches. In other embodiments, the main layer has a thicknessof about 0.018 inches. The auxiliary layer may have a thickness ofbetween about 0.010 inches and about 0.030 inches. In other embodiments,the auxiliary layer has a thickness of about 0.013 inches.

While it is not illustrated that the main layer and the auxiliary layerare attached to a separate control mechanism than the cutting assembly,it is possible for separate controls to be used with the main layer andthe auxiliary layer to enable independent extension and retraction ofthe main layer and the auxiliary layer.

The elongated shaft 40 may be formed with a relatively small outerdiameter to minimize a size of the aperture 20 that needs to be formedin the ilium 14. The larger the aperture 20 that is formed in the ilium14, the greater the fastener size required to gain adequate purchase inthe ilium. In certain embodiments, the outer diameter of the elongatedshaft 40 is between about 6 millimeters and 15 millimeters.

The insertion apparatus 30 may also include a handle portion 42proximate a proximal end thereof. The handle portion 42 enhances theability to manipulate the insertion apparatus 30 such as insertion,rotation and withdrawal.

The handle portion 42 may have a diameter that is greater than adiameter of the elongated shaft 40. In certain embodiments, the handleportion 42 has a diameter of between about 1 centimeter and about 3centimeters.

An outer edge of the handle portion 42 may have a plurality of concaveor convex regions 44 formed therein, or may be made of an elastomericmaterial. The concave regions 44 or elastomeric material enhance theability to grip the handle portion 42 and thereby manipulate theinsertion apparatus 30.

The insertion apparatus 30 may further include a control knob 46 that isused for extending and retracting the cutting assembly 33. In oneconfiguration of the insertion apparatus 30, the control knob 46 isrotatably mounted with respect to the insertion apparatus 30.

The control knob 46 may have a diameter that is different than adiameter of the handle portion 42. Forming the control knob 46 with adiameter that is different than a diameter of the handle portion 42minimizes the potential that a person using the insertion apparatus 30would inadvertently manipulate the insertion apparatus 30 or the controlknob 46.

The control knob 46 may have a diameter that is less than a diameter ofthe handle portion 42. In certain embodiments, the control knob 46 has adiameter of between about 1 centimeter and about 3 centimeters.

An outer edge of the control knob 46 may have a plurality of concaveregions formed therein or may contain an elastomeric material. Theconcave regions or elastomeric material enhance the ability to grip thecontrol knob 46 and thereby manipulate the insertion apparatus 30.

Rotation of the control knob 46 in a first direction causes the cuttingassembly 33 to be extended from the distal end of the insertionapparatus 30. Rotation of the control knob 46 in a second direction,which is opposite the first direction, causes the cutting assembly 33 tobe retracted into the distal end of the insertion apparatus 30.

As an alternative or in addition to manually using the control knob 46to cause retraction of the probe assembly 32, it is possible to use anautomated mechanism in the undercutting system that causes retraction ofthe probe assembly 32.

The automated mechanism can reduce the potential of the probe assembly32 getting hung up if the probe assembly 32 is not at least partiallyretracted while the cutting assembly 33 is extended from the insertionapparatus 30.

The insertion apparatus 30 may also include a locking collar 47 that isoperably attached thereto. The locking collar 47 may be slidably mountedonto the elongated shaft 40 and may initially be positioned proximatethe handle portion 42.

The locking collar 47 may be tightened such that the collar 47 locks inposition along the elongated shaft 40 at a point between the probeassembly 32 and the control knob 46 by, for example, tightening a thumbscrew 49.

The locking collar 47 thereby retains the shaft the elongated shaft 40in a fixed position with respect to a docked working cannula 51 toprevent movement of the insertion apparatus 30 further into the ilium inthe case of drilling past the sacral cortex.

Loosening the locking collar 47 by, for example, loosening the screw 49,allows the locking collar 47 to slide along the elongated shaft 40thereby allowing adjustment of the depth of shaft 40 as required.

Inside at least a portion of the elongated shaft 40 is a controlmechanism 48 that operably attaches the cutting assembly 33 to the otherportions of the insertion apparatus 30, as most clearly illustrated inFIGS. 4 and 5. A primary function of the control mechanism 48 is tofacilitate extension and retraction of the cutting assembly 33.

The control mechanism 48 may generally include an attachment section 62that attaches directly to the cutting assembly 33. The attachmentsection 62 is attached to the control knob 46. In one configuration, theattachment section 62 is fixedly attached to the control knob 46 so thatthe first section 62 rotates when the control knob 46 is rotated.

The attachment section 62 may have a length that is less than the lengthof the elongated shaft 40. In certain embodiments, the attachmentsection 62 has a length that is approximately one-half of the length ofthe elongated shaft 40.

The attachment section 62 may have a generally cylindrical shape with anouter diameter that is slightly smaller than an inner diameter of theelongated shaft 40. Forming the attachment section 62 with this shapefacilitates rotating and sliding of the attachment section 62 withrespect to the elongated shaft 40.

A distal end of the attachment section 62 has a connection mechanism 66that facilitates attaching the cutting assembly 33 to the attachmentsection 62. In one such configuration, the connection mechanism 66includes a recess 70 formed in the distal end. The recess 70 may have awidth and a depth that is greater than a width and a depth of theproximal end of the cutting assembly 33.

An attachment pin 72 may be provided in the recess 70 that enables thecutting assembly 33 to engage the connection mechanism 66. In certainembodiments, the attachment pin 72 may be oriented generallyperpendicular to the attachment section 62.

An aperture may be formed in the proximal end of the cutting assembly33. The aperture may have a diameter that is slightly larger than adiameter of the attachment pin. Using such a configuration, theattachment pin may extend into the aperture to retain the attachmentsection 62 in a fixed relationship with respect to the cutting assembly33.

Forming the connection mechanism 66 with preceding configuration allowsthe cutting assembly 33 to be attached to the attachment section 62 whenthe attachment section 62 and the cutting assembly 33 are not covered bythe elongated shaft 40.

On the other hand, when the elongated shaft 40 is placed over attachmentsection 62 and the cutting assembly 33, the cutting assembly 33 isretained in engagement with the attachment section 62.

A person of skill in the art will appreciate that it is possible toattach the attachment section 62 and the cutting assembly 33 usingdifferent structures, which enable sliding and rotating of theattachment section 62 with respect to the elongated shaft 40.

While the figures illustrate that a mechanical connection is providedbetween the probe assembly 32 and the other components of theundercutting system 10, it is also possible to utilize an electricalconnection between the probe assembly 32 and the other components of theundercutting system 10. Such an electrical connection may utilizeswitches and actuators. It is also possible to use pneumatic andhydraulic systems to operably connect the probe assembly 32 and theother components of the undercutting system 10.

The connection mechanism 66 may also include a ball-type connector 80that attaches the connection mechanism 66 to the attachment section 62.The ball-type connector 80 may include a ball-shaped extension 82 on theconnection mechanism 66 and a recess 84 formed in the distal end of theattachment section 62. The recess 84 has a shape that is generallycomplementary to the shape of the ball-shaped extension 82.

Similar to the attachment between the connection mechanism 66 and thecutting assembly 33, the ball-type connector 80 allows the attachmentsection 62 to be attached to the connection mechanism 66 when theattachment section 62 and the connection mechanism 66 are not covered bythe elongated shaft 40.

On the other hand, when the elongated shaft 40 is placed over attachmentsection 62 and the connection mechanism 66, the ball-shaped extension 82is retained in engagement with the recess 84.

Alternatively or additionally, the undercutting system 10 may includemore than one attachment section 62 having different lengths. Using sucha configuration enables one of the attachment sections 62 to be selectedbased upon the length of the probe assembly 32.

A benefit of using the ball-shaped extension 82 is that this connectionmechanism enables the control handle to rotate such as when extending orretracting the probe assembly 32 with respect to the insertion apparatus30 without having the probe assembly 32 rotate.

The cutting assembly 33 may be formed with a height and a width that areboth slightly smaller than a height and a width of a channel 96 that isformed in an end cap 90, which is discussed in more detail below.Forming the cutting assembly 33 with these dimensions enables thecutting assembly 33 to slide in the channel 96.

The cap 90 may be positioned in the distal end of the elongated shaft40, as most clearly illustrated in FIG. 3. The cap 90 thereby seals theelongated shaft 40 to generally restrict tissue and fluid from enteringthe elongated shaft 40.

While it is possible for a distal end of the cap 90 to be orientedgenerally transverse to the elongated shaft 40, the distal end of thecap 90 may be oriented at an angle of less than about 90 degrees withrespect to the elongated shaft 40. In certain embodiments, the distalend of the cap 90 is oriented at an angle of between about 45 degreesand about 60 degrees.

As referenced above, the cap 90 has the channel 96 formed therein.Proximate the proximal end, the channel 96 may be generally aligned withbut offset from a central axis of the elongated shaft 40. Proximate thedistal end, the channel 96 may be oriented generally perpendicular tothe central axis of the elongated shaft 40 and having a pocket 98 tohouse the main cutter portion 60 and a cutter extension portion 61. Thepocket 98 may have a length and/or a width that are larger than thelength and/or width of the channel 96.

Intermediate the proximal end and the distal end, the channel 96 iscurved. The radius of curvature may be determined by a variety offactors. An example of one such factor is the flexibility of the portionof the probe assembly 32 and the flexibility of a cutting assembly 33,which is described in more detail below.

The channel 96 thereby causes the probe assembly 32 to be deflected suchthat when the probe assembly 32 extends from the cap 90, the probeassembly 32 is oriented in a direction that is generally transverse tothe elongated shaft 40, as illustrated in FIG. 3. This configurationenables the probe assembly 32 to extend into the region between theilium 14 and the sacrum 16.

Because of the flexibility of the cutting assembly 33 and probe assembly32, it is not necessary that the distal end of the channel 96 beoriented precisely transverse to the central axis of the elongated shaft40. For example, the distal end of the channel 96 may be orientedslightly towards the ilium 14 to encourage preferential cutting of theilium 14 because the ilium 14 is harder than the sacrum 16.Alternatively, orienting the distal end of the channel 96 slightlytowards the sacrum 16 may encourage preferential cutting of the sacrum16 and allow the angle of curvature within the cap to be reduced.

As an alternative to, or in conjunction with, utilizing flexibility ofthe probe assembly 32 and/or the cutting assembly 33 to facilitatetracking of the joint between the ilium 14 and the sacrum 16, it ispossible for at least a portion of the cap 90 to swivel. The cap couldtrack the joint itself, or could track a ring on a guide at the bottomof the insertion apparatus 30.

Such a configuration enables the user to angle the guide to align theguide with the joint as viewed using an imaging technique such asfluoroscopy. Once a proper alignment is obtained, the guide may belocked into place so that the probe assembly 32 and the cutting assemblytracks the guide.

In certain embodiments, the cap 90 is fabricated from a radiolucentmaterial such as aluminum. Fabricating the cap 90 in this manner enablesimaging such as fluoroscopy to be used to monitor the location of theend of the cutting assembly 33 throughout the undercutting process suchas when the distal end of the cutting assembly 33 is in the retractedposition.

The cap 90 may have a positive feature that is generally perpendicularto the axis of the elongated shaft 40. The elongated shaft 40 may alsoinclude an aperture that is generally aligned with the positive featurewhen the cap 90 is placed into the distal end of the elongated shaft 40.A screw is extended across the cap 90 thereby forcing the positivefeature of the cap 90 into the aperture in the elongated shaft 40retaining the cap 90 in a stationary position with respect to theelongated shaft 40.

The cutting assembly 33 may be used in conjunction with the probeassembly 32. As is described in more detail herein, the probe assembly32 facilitates identifying the joint line between the ilium 14 and thesacrum 16. Thereafter, the cutting assembly 33 cuts tissue between theilium 14 and the sacrum 16 to prepare for the sacroiliac fusion.

To permit the deflection of the cutting assembly 33, the cuttingassembly 33 may be fabricated from a flexible material, as is discussedin more detail below. To increase the flexibility of the cuttingassembly 33, a plurality of kerfs or notches 53 may be formed in thecutting assembly 33.

While the kerfs 53 are utilized to provide flexibility to the cuttingassembly 33, the number and placement of the kerfs 53 should be selectedto minimize negative impact on the strength of the cutting assembly 33.

As illustrated in FIGS. 6 and 7, the kerfs 53 may extend through anupper surface 50 of the cutting assembly 33. The kerfs 53 may alsoextend through at least a portion of at least one of the side surfaces52 of the cutting assembly 33. In certain embodiments, the kerfs 53extend substantially through both of the side surfaces 52. The kerfs 53may also extend into a lower surface 54 of the cutting assembly 33.

Forming the kerfs 53 with the preceding configuration allows a lowersurface 54 of the cutting assembly 33 to be substantially continuous.This configuration provides the cutting assembly 33 with sufficientstrength to resist breaking while the cutting assembly 33 is used to cuttissue from between the ilium 14 and the sacrum 16.

The kerfs 53 may be formed with a width that is sufficiently large sothat the material remaining between the kerfs 53 does not impinge uponitself while the cutting assembly 33 is deflected from the initialorientation that is generally aligned with but offset from the centeraxis of the insertion apparatus 30 to a deflected orientation that isgenerally transverse to the central axis of the insertion apparatus, asthe cutting assembly 33 exits the distal end of the cap 90.

In certain embodiments, the kerfs 53 may have a width of up to about 1.5millimeters. In other embodiments, the kerfs 12 may have a width that isbetween about 0.6 millimeters and about 1 millimeter.

The kerfs 53 also decrease the smoothness of the cutting assembly 33.Contact between the kerfs 53 and the tissue between the ilium 14 and thesacrum 16 could cause such tissue to be abraded or cut and therebyfacilitate preparation of the region between the ilium 14 and the sacrum16 for the sacroiliac fusion process.

While the figures illustrate that the kerfs 53 are formed on one side ofthe cutting assembly 33, it is possible for the kerfs 53 to be formed onboth sides of the cutting assembly 33. If the kerfs 53 are formed onboth sides of the cutting assembly 33, the kerfs 53 on the oppositesides may be offset so that the kerfs 53 do not unduly weaken thecutting assembly 33.

Whether the kerfs 53 are formed in one side or both sides of the cuttingassembly 33, the kerfs 53 should not occupy too great a portion of thecutting assembly 33 such that the cutting assembly 33 is likely to bendor kink during the process of deflecting during the extension orretraction of the cutting assembly 33 from the insertion apparatus 30 aswell as during the use of the cutting assembly 33 to cut tissue frombetween the ilium 14 and the sacrum 16.

An alternative embodiment of the invention utilizes kerfs 53 having anangular configuration, as illustrated in FIGS. 8 and 9, which is to bedistinguished from the kerfs 53 that are oriented generallyperpendicular to a lower surface of the cutting assembly 33, asillustrated in FIGS. 6 and 7.

The angle of the kerfs 53 may be between about 20 degrees and about 70degrees. In certain embodiments, the angle of the kerfs 53 is betweenabout 25 degrees and about 35 degrees. In still other embodiments, theangle of the kerfs 53 is about 30 degrees.

Each kerf 53 may have a thickness that is substantially constant betweena proximal end and a distal end thereof. In other embodiments, the kerfs53 have a thickness that is greater proximate the distal end thanproximate the proximal end, as illustrated in FIG. 8. In certainembodiments, the thickness of each kerf 53 proximate the distal end isabout twice the thickness of the kerf 53 proximate the proximal end.

Similar to the embodiment illustrated in FIGS. 6 and 7, the spacingbetween adjacent kerfs 53 should be sufficiently large such thatmaterial between adjacent kerfs 53 does not impinge upon itself when thecutting assembly 33 is moved from the retracted position where thecutting assembly 33 is oriented generally parallel to the central axisof the insertion apparatus 30 to the extended position where at leastthe distal portion of the cutting assembly 33 is oriented generallyperpendicular to the central axis of the insertion apparatus 30.

In certain embodiments, the thickness of the kerf 53 proximate thedistal end may be greater than a separation between adjacent kerfs 53and the thickness of the kerf 53 proximate the distal end may be lessthan a separation between adjacent kerfs 53.

The separation between adjacent kerfs 53 may be between about 0.5millimeters and about 0.75 millimeters. In other embodiments, theseparation between adjacent kerfs 53 is about 0.6 millimeters.

The thickness of the kerf 53 proximate the distal end may be between 0.5millimeters and about 0.9 millimeters. In other embodiments, thethickness of the kerf 53 proximate the distal end is about 0.7millimeters. Between about 20% and about 80% of the length of the kerf53 has the greater thickness. In other embodiments, between about 30%and 50% of the length of the kerf 53 has the greater thickness.

The corners between the wide and narrow sections of the kerf 53 andproximate the intersection of the kerf 53 and the lower surface 54 maybe rounded. In certain embodiments, the rounded corners have a radius ofbetween about 0.125 millimeters and about 0.5 millimeters. In otherembodiments, the radius is about 0.25 millimeters.

The embodiment of the cutting assembly 33 illustrated in FIGS. 6 and 7could be modified to include the kerfs 53 having a thickness that isgreater proximate the distal end than the proximal end thereof asillustrated by the left most opening on the cutting assembly illustratedin FIG. 7.

Forming the kerf 53 with the preceding configuration enhances the amountof the lower surface 54 of the cutting assembly 33 to which the sidesurfaces 52 have been removed, which thereby increases the length of thelower surface 54 that is bent. This configuration decreases stressconcentrations and the associate metal fatigue and thereby increases theuseful life of the cutting assembly 33.

The cutting assembly 33 may be supported by the probe assembly 32, whichextends through the cutting assembly 33, to thereby enhance the strengthof the cutting assembly 33. The cutting assembly 33 having the precedingshape and characteristics may be formed from a variety of materials. Aperson of skill in the art will appreciate that the material used tofabricate the cutting assembly 33 should be suitable for use within ahuman body. An example of one such material for fabricating the cuttingassembly 33 is stainless steel.

At least one cutting element 34 may be provided on the cutting assembly34. The cutting element 34 may be positioned proximate the distal end ofthe cutting assembly 33. In certain embodiments, the cutting element 34may include a main cutter portion 60 and at least one cutter extensionportion 61 that extends from the main cutter portion 60.

In certain embodiments, the sacroiliac fusion system may includemultiple undercutting systems 10. Each of the undercutting systems 10may include a main cutter portion 60 having a different height and bemounted on different sides of the cutting assembly 33. Using such aconfiguration, the undercutting system 10 can be alternatively used atdifferent stages of the process.

One such undercutting system 10 includes the main cutter portion 60 onthe side of the cutting assembly 33 that is oriented towards the iliumafter the cutting assembly 33 is deployed from the insertion apparatus30. Another such undercutting system 10 includes the main cutter portion60 on the side of the cutting assembly 33 that is oriented towards thesacrum after the cutting assembly 33 is deployed from the insertionapparatus 30.

Still another undercutting system 10 includes the main cutter portion 60that extends from opposite sides of the cutting assembly 33 such thatthe main cutter portions 60 are oriented towards the sacrum and theilium after the cutting assembly 33 is deployed from the insertionapparatus 30.

The main cutter portion 60 may have a height that is greater than theheight of the cutting assembly 34. The main cutter portion 60 therebyenables a region between the ilium 14 and the sacrum 16 having a greaterthickness to be prepared.

The main cutter portion 60 may have a height that is no greater than thecorresponding pocket in the cap 90. Forming the main cutter portion 60with such a configuration enables the cutting assembly 33 to bepositioned substantially within a profile of the elongated shaft 40 whenthe cutting assembly 33 is in a retracted configuration so that thecutting assembly 33 does not interfere with the insertion of the distalend of the undercutting system 10 extending through the aperture 20 inthe ilium 14.

The main cutter portion 60 may have a height of between about 1millimeter and about 3 millimeters. In certain embodiments, the maincutter portion 60 may have a width of about 2 millimeters.

Similarly, the main cutter portion 60 may have a width that is nogreater than an inner diameter of the elongated shaft 40. Forming themain cutter portion 60 with such a configuration enables the cuttingassembly 33 to be positioned substantially within a profile of theelongated shaft 40 when the cutting assembly 33 is in a retractedconfiguration so that the cutting assembly 33 does not interfere withthe insertion of the distal end of the undercutting system 10 extendingthrough the aperture 20 in the ilium 14.

The main cutter portion 60 may have a width of between about 2millimeters and about 5 millimeters. In certain embodiments, the maincutter portion 60 may have a width of about 3 millimeters.

The main cutter portion 60 may be curved proximate each of the cornersthereof. Using the curved corners reduces the potential of the maincutter portion 60 digging too deeply into the surface of the ilium 14 orthe sacrum 16 while the cutting assembly 33 is rotated.

In other embodiments, where it is desired to enhance the cutting abilityof the cutting assembly 33, the main cutter portion 60 may be formedwith sharp corners and at least a portion of the surface of the cornersmay be sharpened to enhance the cutting ability of the main cutterportion 60.

The main cutter portion 60 has a distal edge and a proximal edge thatare disposed at opposite ends thereof. In certain embodiments, thedistal edge and the proximal edge may be sufficiently sharp to cutthrough the tissue between the ilium 14 and the sacrum 16 that comesinto contact with at least one of the distal edge and the proximal edge.

Alternatively, at least one of the distal edge and the proximal edge mayinclude a cutting surface. In certain embodiments, cutting surfaces areprovided on both distal and proximal edges of the main cutter portion60. Providing the cutting surfaces on the distal and proximal edgesenhances the ability of the main cutter portion 60 to cut through tissuebetween the ilium 14 and the sacrum 16 as the cutting assembly 33 isrotated.

As an alternative to or in addition to sharpening the main cutterportion 60, an abrasive surface may be provided on at least a portion ofthe outer surface of the main cutter portion 60. Examples of theabrasive surface include chemical etching and sintering material such asbeads on the main cutter portion 60. Alternatively or additionally, themain cutting portion 60 may have a plurality of bristles extendingtherefrom.

The cutter extension portion 61 may have a generally planarconfiguration that extends from at least one of the upper and lowersurfaces of the main cutter portion 60. While not illustrated, it isalso possible for at least one of the cutter extension portions 61 to bepositioned on the side surfaces of the main cutter portion 60.

In certain embodiments, the cutter extension portion 61 may extend insubstantially equal distances on opposite sides of the main cutterportion 60. The cutter extension portion 61 may have a generallyrectangular shape that is defined by a distal edge and a pair of sideedges.

While it is illustrated that a height of the cutter extension portion 61is approximately equal on opposite sides of the main cutter portion 60,it is possible to configure the cutter extension portion 61 so that theheight of the cutter extension portion 61 is not approximately equal onopposite sides of the main cutter portion 60. Such a configuration maybe used to preferentially cut one of the ilium 14 and the sacrum 16.

The height of the distal edge may be limited by the inner diameter ofthe elongated shaft 40 so that the cutting element 34 may be retractedwithin the insertion apparatus 30 when the insertion apparatus 30 isinserted into and removed from the region between the ilium 14 and thesacrum 16.

In certain embodiments, the height of the cutter extension portion 61 onopposite sides of the main cutter portion 60 is between about 1millimeter and about 5 millimeters. In other embodiments, the height ofthe cutter extension portion 61 on opposite sides of the main cutterportion 60 is about 3 millimeters.

In certain embodiments, a width of the cutter extension portion 61 isapproximately the same on opposite sides of the main cutter portion 60.The width of the cutter extension portion 61 may be between about 1millimeter and about 5 millimeters. In other embodiments, the width ofthe cutter extension portion 61 is about 3 millimeters.

Corners proximate the intersection of the distal edge and each of theside edges may be curved. While such curvature could reduce the cuttingability of the cutter extension portion 61 that could be attained if thedistal edge and the side edge intersected at a corner, this curvaturemay reduce the tendency of the cutter extension portion 61 to dig toodeeply into the surfaces of the ilium 14 and the sacrum 16. As a resultof this configuration, the cutter extension portion 61 wouldpreferentially cut into the tissue between the ilium 14 and the sacrum16 as opposed to cutting the ilium 14 and the sacrum 16.

While it is illustrated that the cutter extension portion 61 has asubstantially equal thickness, it is possible for the thickness of thecutter extension portion 61 to vary. In certain embodiments, thethickness of the cutter extension portion 61 may be greater proximate tothe main cutter portion 60 to resist bending or deformation of thecutting element 34.

In certain embodiments, a thickness of the cutter extension portion 61may be between about 0.2 millimeters and about 2 millimeters. In otherembodiments, the thickness of the cutter extension portion 61 may beabout 0.5 millimeters.

While it is illustrated that the thickness of the cutter extensionportion 61 is approximately equal on opposite sides of the main cutterportion 60, it is possible to configure the cutter extension portion 61so that the thickness of the cutter extension portion 61 is notapproximately equal on opposite sides of the main cutter portion 60.

The edge of the cutter extension portion 61 proximate the distal endsthereof may be sufficient to cut through the tissue between the ilium 14and the sacrum 16. Using the cutter extension portion 61 without thesharpened edges may reduce a tendency of the cutter extension portion 61to cut too deeply into the ilium 14 and the sacrum 16 while the cuttingassembly 33 is rotated.

Alternatively, the edge of the cutter extension portion 61 proximate thedistal ends thereof may be sharpened to facilitate cutting of tissueproximate the surfaces of the ilium 14 and the sacrum 16 while thecutting assembly 33 is rotated.

As an alternative to or in addition to sharpening the cutter extensionportion 61, an abrasive surface may be provided on at least a portion ofthe outer surface of the cutter extension portion 61. Examples of theabrasive surface include chemical etching and sintering material such asbeads on the cutter extension portion 61. Alternatively or additionally,the cutter extension portion 60 may have a plurality of bristlesextending therefrom.

The cutter extension portion 61 may be oriented generally parallel tothe length of the cutting element 34. In other embodiments, the cutterextension portion 61 may be oriented at an angle of between about 0degrees and about 60 degrees with respect to a length of the cuttingelement 134. In other embodiments, the angle between the cutterextension portion 61 and the main cutter portion 60 may be about 30degrees.

Orienting the cutter extension portion 61 at the angle with respect tothe length of the main cutter portion 60 causes one of the edges to bedisposed forwardly. Such a configuration may increase the ability of thecutting element 34 to cut tissue from between the ilium 14 and thesacrum 16 as the cutting assembly 33 is rotated.

While it is illustrated that the cutter extension portion 61 is orientedgenerally transverse to the surface of the main cutter portion 60, it ispossible for the cutter extension portion 61 to be oriented at an anglewith respect to the surface of the main cutter portion 60. For example,the cutter extension portion 61 may be oriented at an angle of betweenabout 30 degrees and 60 degrees towards either a distal end or aproximal end of the cutting assembly 33. Using such a configurationenables the cutter extension portion 61 to also cut by scraping into thetissue.

While it is possible for the cutting element 34 to be placed at thedistal end of the cutting assembly 33, in certain embodiments, thecutting element 34 may be mounted a distance from the distal end of thecutting assembly 33. Mounting the cutting element 34 a distance from thedistal end of the cutting assembly 33 enables the cutting assembly 33 todefine a path through the tissue between the ilium 14 and the sacrum 16,as opposed to the cutting element 34 being the primary component thatdefines the path through the tissue between the ilium 14 and the sacrum16.

The cutter extension portion 61 may be positioned at a location that isapproximately intermediate between the side edges of the main cutterportion 60. Placing the cutter extension portion 61 in this location mayreduce twisting of the cutting assembly 33, which could potentiallyoccur if the cutter extension portion 61 was located closer to one ofthe side edges of the main cutter portion 60.

The cutting element 34 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting element34 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting element 34 is stainless steel.

In certain embodiments, the cutting assembly 33 may be fabricatedseparately from the cutting element 34. Forming the structure in thismanner enables different materials to be used for fabricating thecutting assembly 33 and the cutting element 34 so that the respectivematerials may be optimized based upon the function of the associatedstructure.

The cutting element 34 may be attached to the cutting assembly 33 usinga variety of techniques that cause the cutting element 34 to be fixedlyattached to the cutting assembly 33. One such suitable technique forattaching the cutting element 34 to the cutting assembly 33 is welding.

Alternatively, it is possible to fabricate the cutting assembly 33 andthe cutting element 34 as a single unit such as by machining a block toprovide a substantially flat cutting assembly 33 and a cutting element34 that extends from the cutting assembly 33.

The undercutting system 10 may include a plurality of cutting assemblies33 with cutting elements 34 having different distances heights. One ofthe cutting assemblies 33 with the cutting element 34 having thesmallest height may be initially used. Thereafter, cutting assemblies 33with cutting elements 34 having progressively larger heights may be usedto form a progressively higher region between the ilium and the sacrum.

In addition to or in an alternative to forming the cutting elements 34with different thicknesses, it is possible to use a series of cuttingelements 34 to facilitate preparing the surfaces of the ilium 14 and thesacrum 16 in a predictable manner. In one such configuration, there is aseries of three cutting elements 34 used to prepare the region betweenthe ilium 14 and the sacrum 16.

The different cutting elements 34 can be part of a separate undercuttingsystem 10 such as described above. Alternatively, the different cuttingelements 34 to be alternatively connected to the insertion apparatus 30

The first cutting element 34 may be configured to preferentially cuttissue on the ilial side of the first cutting element 34. The firstcutting element 34 may have one extension portion 61 that is positionedon the ilial side of the first cutting element 34.

The cutter extension portion 61 may have a first height that extendsabove a surface thereof. In certain embodiments, the cutter extensionportion 61 may have a height of about 0.5 millimeters. The overallheight of the first cutting element 34 is thereby about 2.5 millimeters.

Because the cutter extension portion 61 is on the ilial side of thefirst cutting element 34, this configuration may exhibit beneficialperformance characteristics because this configuration accounts for thefact that a surface of the ilium 14 is harder than a surface of thesacrum 16.

The second cutting element 34 may also include one cutter extensionportion 61 that is positioned on the sacral side of the first cuttingelement 34. The cutter extension portion 61 on the second cuttingelement 34 may have a height that is greater than the height of thecutter extension portion 61 on the first cutting element 34.

The cutter extension portion 61 may have a second height that extendsabove a surface thereof. In certain embodiments, the cutter extensionportion 61 may have a height of about 0.5 millimeters. The overallheight of the first cutting element 34 is thereby about 2.5 millimeters.

The configuration of the second cutting element 34 thereby enables anincreased distance area between the ilium 14 and the sacrum 16 to beprepared, as compared to the first cutting element 34. However, similarto the first cutting element 34, the second cutting element 34preferentially cuts on the ilial side of the second cutting element 34.

The third cutting element 34 may have an extension portion 61 that ispositioned on the ilial and sacral sides thereof. While it is possiblefor the extension portions 61 to have different heights, in certainembodiments, the extension portions 61 each have a height of about 1millimeter. The overall height of the third cutting element 34 isthereby about 4 millimeters.

Because the extension portions 61 are positioned on the ilial and sacralsides of the third cutting element 34, the third cutting element cutstissue that is located on the ilial and sacral side of the third cuttingelement 34.

The cutting assembly 33 may be operably attached to the insertionapparatus 30 to facilitate extension and retraction of the cuttingassembly 33 with respect to the insertion apparatus 30. In oneembodiment, a control is provided for movement of the cutting assembly33 that is separate from the control knob 46 used to move the probeassembly 32.

The cutting assembly control may be a knob 76 that is mounted to theinsertion apparatus. Similar to the control knob 46, rotation of thecutting assembly control knob 76 in a first direction may causeextension of the cutting assembly 33 from the insertion apparatus 30 androtation of the cutting assembly control knob 76 in a second directionmay cause retraction of the cutting assembly 33 into the insertionapparatus 30.

In another embodiment, the probe assembly 32 and the cutting assembly 33are both operably connected to the control knob 46. When the controlknob 46 is initially rotated, the probe assembly 32 is extendedprogressively further from the insertion apparatus 30. Once the probeassembly 32 reaches its maximum extension, continued rotation of thecontrol knob 46 causes the cutting assembly 33 to be extended from theinsertion apparatus 30.

The distal end of the probe assembly 32 extends beyond the distal end ofthe cutting assembly 33 when these components are extended from thedistal end of the insertion apparatus 30. Using this configurationenables the probe assembly 32 to guide the cutting assembly 33 andthereby reduce the potential of the cutting assembly 33 digging toodeeply into the ilium 14 or the sacrum 16.

Once the probe assembly 32 has been extended the maximum distance fromthe distal end of the insertion apparatus 30 and the insertion apparatus30 has been rotated at least one full revolution so that the probeassembly 32 has caused the path between the ilium 14 and the sacrum 16to be defined, it may be possible for the cutting assembly 33 to befully extended so that the distal end of the cutting assembly 33 is atapproximately the same distance from the distal end of the insertionapparatus 30 as the probe assembly 32.

When the surgical procedure is completed and it is desired to remove theundercutting system 10, the control knob 46 is rotated in an oppositedirection. This rotation initially causes retraction of the cuttingassembly 33.

Once the cutting assembly 33 is fully retracted, continued rotation ofthe control knob 46 causes the probe assembly 32 to be retracted. Afterboth the probe assembly 32 and the cutting assembly 33 are fullyretracted within the insertion apparatus 30, the undercutting system 10may be removed from the patient.

Using the probe assembly 32 in conjunction with the cutting assembly 33enables the region between the ilium 14 and the sacrum 16 to be preparedfor the sacroiliac fusion while minimizing the cutting assembly 33digging too deeply into the surface of the ilium 14 or the sacrum 16.

While it is desirable to prepare the surfaces of the ilium 14 and thesacrum 16 by exposing bleeding bone, it is desirable to avoid thecutting assembly 33 digging into the surface of the ilium 14 or thesacrum 16 too deeply. When the cutting assembly 33 digs too deeply intothe surface of the ilium 14 or the sacrum 16, it becomes more difficultto rotate the cutting assembly 33 because the ilium 14 and the sacrum 16are much harder than the tissue located between the ilium 14 and thesacrum 16. The cutting assembly 33 having the characteristics set forthabove meets these criteria.

To minimize the potential of the cutting assembly 33 breaking during thecutting process, a clutch mechanism may be provided between the handleand the cutting assembly 33. The clutch mechanism causes the operableconnection between the handle 42 and the cutting assembly 33 to releasewhen greater than a threshold force is encountered. When this occurs,the handle 42 rotates with respect to the cutting assembly 33.

An audible notification may be provided to indicate to the person usingthe undercutting system 10 that the clutch has been engaged. An exampleof which such audible notification is a scratching or clicking soundthat is sufficiently loud to be heard outside of the patient.

After the clutch has been activated, the person operating the cuttingassembly 33 may rotate the cutting assembly 33 in an opposite directionor partially retract the cutting assembly 33. Thereafter, the cuttingprocess may be resumed.

Another configuration of the cutting assembly does not include a kerfedtube that extends over a probe assembly as described above. Rather, thecutting assembly utilizes a multiple strip design.

The multiple strip cutting assembly may include a central strip that isfabricated from a flexible material such as nitinol or stainless steel.The central strip may be similar to the probe assembly discussed above.An outer strip is attached to at least one surface of the central strip.In certain embodiments, the outer strip is attached to both sides of thecentral strip.

The outer strip may have a width that is similar to the width of thecentral strip. In other embodiments, the outer strip may have a widththat is greater than or less than the width of the central strip.

The outer strips may be formed from a material that is different thanthe material from which the central strip is fabricated. In certainembodiments, the outer strips are fabricated from a more rigid materialthan the material that is used to fabricate the central strip. Formingthe outer strips from a more rigid material than the central strip mayenhance the cutting ability of the cutting assembly produced accordingto this embodiment. In certain embodiments, the outer strips arefabricated from stainless steel.

The outer strips are attached to the central strip so that the centralstrip and the outer strips move as a unit. Alternatively, the outerstrips may move together and the inner strip may move independently, aswith the independent operation of the probe assembly 32 and cuttingassembly 33 described above. An example of one technique that may beused to attach the outer strips to the central strip is welding.

At least one cutting element may extend from each of the outer strips.The cutting element may have a similar configuration to the cuttingelements that are used in conjunction with the cutting assemblyillustrated in FIGS. 1-5.

As an alternative to or in addition to the cutting elements, an abrasivesurface may be provided on at least a portion of the outer surface ofthe cutting elements. Examples of the abrasive surface include chemicaletching and sintering material such as beads on the cutting elements. Instill other configurations, the cutting elements may include a pluralityof bristles extending therefrom.

An advantage of the preceding configuration is that the cutting assemblyhas reduced complexity compared to the cutting assembly utilizing thekerfed tube. Additionally, this configuration does not include stressconcentration points that are present where the kerfs are cut into thetube of the cutting assembly illustrated in FIGS. 6-7.

A disadvantage of the preceding configuration is that the cuttingassembly has a reduced ability to carry cut tissue that enters thekerfs. Additionally, there is no incidental scratching of tissue withthe kerfed region, which enhances the cutting performance.

As a preliminary step in the use of the undercutting system 10 inconjunction with performing a sacroiliac fusion, the undercutting system10 is sterilized. In certain embodiments, the sterilization is performedusing steam. Prior to placing the undercutting system 10 in the steamsterilization unit, the probe assembly 32 and the cutting assembly 33are moved to the extended position.

If the probe assembly 32 and the cutting assembly 33 are in theretracted position during the steam sterilization process, the heatassociated with the steam may cause the distal ends of the probeassembly 32 and/or the cutting assembly 33 to become heat set.

Having the distal ends of the probe assembly 32 and the cutting assembly33 become heat set is undesirable because the distal ends of the probeassembly 32 and the cutting assembly 33 would move in a curved pathwhile performing the undercutting procedure, which corresponds to theheat set curvature as opposed to tracking in a generally lineardirection between the ilium 14 and the sacrum 16.

To facilitate use of the undercutting system 10 and the performance ofthe sacroiliac fusion, the patient on which the sacroiliac fusion is tobe performed may be positioned in a prone or supine orientation on anoperating room table or other support structure that is used inconjunction with this procedure.

While it is possible to form a relatively large incision and then pullback the tissue between the skin and the ilium so that the surface ofthe ilium could directly be viewed when using the undercutting system 10of the invention, such a process could cause more damage to the tissuebetween the skin and the ilium, which could increase the time for thepatient to recover from the surgical procedure.

The tissue penetrated when using the method discussed herein may include(when moving from lateral to medial)—skin, gluteus maximus, gluteusmedius, gluteus minimus, lateral ilium cortex, medial ilium cortex,sacroiliac joint cartilage (ilium and sacrum), lateral sacral cortex,sacral ala, sacral vestibule (which is also known as alar root, sacralpedicle and sacral isthmus) and sacral vertebral body.

Other critical soft tissue that is proximate to where the undercuttingsystem 10 is being used may include (when moving from lateral tomedial)—superior cluneal nerves, superior gluteal artery and vein, L4,L5, S1 and S2 nerve roots, iliac artery, iliac vein, sacral foris alsoknown as neuroforamina), bowels and sacral canal.

Additional relevant anatomical landmarks that have not been previouslymentioned include greater sciatic notch, alar slope and iliac corticaldensity, sacral prominence, pubic symphysis, pelvic brim/arcuate lineand S1 end plate.

A variety of techniques may be used to determine the location at whichthe first aperture 20 and the second aperture 20 are to be formed in theilium as well as the orientation of the ilium so that the first aperture20 and the second aperture 20 may be in a desired position and notresult in damage to the tissue adjacent to and/or above where the firstaperture 20 and the second aperture 20 are to be formed.

A non-limiting example of a technique that may be used to determine thelocation and orientation of the first aperture 20 and second aperture 20is a fluoroscope. To assist in evaluating the location and orientationof the anatomical structures proximate to where the undercutting system10 will be used, it is possible to perform the fluoroscopic imaging frommultiple directions.

One such direction for the fluoroscopic imaging is a lateral view acrossthe patient's pelvis. The lateral sacral view provides a visualizationof the starting point for the sacroiliac joint access by best showingcritical boundaries of the safe bony corridor such as the anteriorsacral cortex and the alar slope.

While less clear but also visible, the lateral sacral view provides theability to see the sacral neural foramina and the spinal canal. Thelateral view along with the outlet view can help to identify sacraldysmorphism, a challenging anatomical variation.

The lateral view may be obtained by aligning the projections of the twogreater sciatic notches and the two iliac cortical densities. Tominimize the x-ray exposure, it is not necessary for there to be exactalignment of the preceding elements.

If the greater sciatic notches and the iliac cortical densities are notsimultaneously aligned, it is possible to split the difference betweenthese components. Alternatively, when alignment of the iliac corticaldensities is difficult, alignment of the greater sciatic notches may besufficient for performing the lateral fluoroscopic image.

It should also be noted that when aligning for the lateral view, truelateral of the sacrum may not appear to be true lateral to the patient.For the purposes of this invention, the important facture is thealignment of the sacrum.

Another view for the fluoroscopic imaging is an anteroposterior viewwith a caudal tilt. This view, which is referred to as the inlet view,may provide an excellent mediolateral view of the advancing guide pinand/or bone screw. This view also best enables avoidance of theposterior spinal canal and the anterior limit of the sacrum.

The inlet view is used in conjunction with the outlet view, which isdescribed below, while advancing the guide pin or bone screw mediallyinto the patient. Together the inlet view and the outlet view provideorthogonal images to guide screw insertion in all three dimensions.

The inlet view is obtained by tilting the fluoroscopic receiver caudalfrom the anteroposterior position. The device is aligned with a linecreated by the anterior-inferior sacral cortex and the iliac pelvic brimwith the second foramina. To minimize the x-ray exposure, it is notneeded for there to be perfect alignment of the inlet view.

Still another view of the fluoroscope imaging is an anteroposterior viewwith a cephalad tilt. This view, which is referred to as the outletview, may provide an excellent mediolateral view of the advancing guidepin and bone screw towards the center of the sacral body. The outletview enables avoidance of the Superior S1 end-plate and the S1neuroforamina.

The outlet view may be used in conjunction with the inlet view whileadvancing the guide pin or bone screw medially into the patient. Whenviewed together, the inlet view and the outlet view provide nearlyorthogonal image to guide screw insertion in all three dimensions.

The outlet view is best suited for viewing the sacroiliac joint tofacilitate cartilage excision. While the outlet view may be similar to a“Judet” view, it is distinct from such a view and, as such, these viewsare not interchangeable.

The outlet view can be used to assure that the tip of the guide pin iscephalad to the sacral nerve foramen. The outlet view also distinguishesthe cephalad border of the sacrum, which is actually the posteriorsacral alar region. The anterior aspects of the sacral ala are slopedinferiorly relative to the posterior sacral alar region. The failure toaccount for this forward sloping could result in the extraosseusinstrument or screw placement being dangerously close to the iliacvessels and/or the fifth lumbar nerve root.

The outlet view may be obtained by tilting the fluoroscope receivercephalad from an anteroposterior position until the top of the symphysispubis is located at the S2 body. To minimize x-ray exposure, it is notneeded for there to be perfect alignment of the outlet view.

As an initial point in locating a location for access, a relativelysmall guide pin such as having a length of about 3 millimeters is heldto the outside of the patient proximate to the location of theiliosacral corridor. The tip of the guide pin may be positioned caudalto the iliac cortical density and cephalad to the interosseous path ofthe upper sacral nerve root.

The lateral projection of the iliosacral corridor identifies the safestposition for the distal end of the bone screw that is insertedlaterally. The proximal entry point may be outside the iliosacralcorridor.

The guide pin tip can be located within the midportion of the alar boneon the lateral image. The iliosacral corridor is the best location forpassage of the bone screw using in conjunction with the sacroiliacfusion.

After marking the skin, a vertical incision having a length of betweenabout 2 and 4 centimeters is formed in the skin. Next, using bluntdilation, a probe is extended through the tissue in line with the futurepath of the screw until reaching the ilium bone.

The most effective area for joint preparation may be theinferior-anterior edge of the safe zone closer to the articularcartilage portion of the joint as opposed to the interosseous portiondirectly lateral of the safe zone.

The articular portion of the joint is more flat, which is advantageousto encourage fusion at the articular portion of the sacroiliac joint. Incontrast, the interosseous portion of the joint, which is posterior tothe safe zone, is steeply angulated from perpendicular, and very lumpyand irregular.

After appropriate preparation of the patient and identification of thelocation for the sacroiliac fusion, at least one aperture 20 is drilledthrough the ilium 14. This aperture 20 may also at least partiallyextend into the sacrum 16, as illustrated in FIG. 10. In certainembodiments, there are three apertures drilled.

Even though FIG. 10 illustrates that the procedure is performed byinitially drilling into the ilium 14, it is also possible to perform thesacroiliac fusion by initially drilling into the sacrum 16. In certaincircumstances, it may present fewer challenges in gaining access for thesacroiliac fusion by initially drilling into the ilium 14.

A conventional surgical drill 92 and drill bit 94 may be utilized toform the aperture 20. The aperture 20 may be formed with a diameter thatis selected based upon a diameter of the insertion apparatus 30 thatwill be inserted into the aperture 20 as part of the undercuttingprocess.

As illustrated in FIG. 10, the drill 92 may be oriented generallytransverse to a surface of at least one of the ilium 14 and the sacrum16 proximate to where the aperture 20 is being formed. A person of skillin the art will appreciate that neither the ilium 14 nor the sacrum 16are substantially flat. Additionally, the adjacent surfaces of the ilium14 and the sacrum 16 may not be substantially parallel to each otherproximate to where it is desired to form the aperture 20.

The aperture 20 may be oriented generally transverse to the ilium 14. Asused herein, generally transverse means that an angle between theaperture 20 and the ilium 14 proximate to where the aperture 20 isformed is between about 45 degrees and about 90 degrees. In otherembodiments, the angle is between about 60 degrees and about 90 degrees.The orientation of an inner surface of the ilium 14 is more importantthan the orientation of an outer surface of the ilium 14.

The apertures 20 may include a first aperture 20 that is used inconjunction with a first screw having a diameter of about 12.5millimeters. In this situation, the drill bit used to form the firstaperture 20 may have a diameter of approximately 9 millimeters.

The first aperture 20 may be formed across the sacroiliac joint at theS1 level. The first aperture 20 may be positioned to favor ananterior-inferior side of the sacroiliac joint. The first aperture 20may be oriented at an angle so that the distal end of the first screw isslightly posterior and superior of a proximal end of the first screw.

The apertures 20 may also include a second aperture 20 that is used inconjunction with a second screw having a diameter of about 6.5millimeters. In this situation, the drill bit used to form the secondaperture 20 may have a diameter of approximately 4 millimeters.

The second aperture 20 may be formed across the sacroiliac jointproximate to where the first aperture 20 is formed in the sacroiliacjoint. The second aperture 20 may be oriented at an angle so that thedistal end of the second screw is slightly anterior and superior to aproximal end of the second screw.

Next, the undercutting system 10 is positioned in a retractedconfiguration so that the probe assembly 32 does not interfere with theinsertion process. The distal end of the undercutting system 10 isextended into the aperture 20, as illustrated in FIG. 11.

Once the distal end of the undercutting system 10 is positioned betweenthe ilium 14 and the sacrum 16, the probe assembly 32 is moved to an atleast partially extended configuration, as illustrated in FIG. 12.

The undercutting system 10 is rotated to so that the probe assembly 32causes a path to be defined between the ilium 14 and the sacrum 16. Bydefining the path using the probe assembly 32, the potential of thecutting assembly 33 digging too deeply into the ilium 14 or the sacrum16 is reduced.

Next, the cutting assembly 33 is extended over the probe assembly 32until the cutting element 34 extends from the distal end of theinsertion apparatus 30 and is positioned between the ilium 14 and thesacrum 16. The undercutting system 10 is rotated so that the cuttingelement 34 contacts tissue between the ilium 14 and the sacrum 16 tocause such tissue to be cut into pieces.

Alternatively or additionally, the cutting element 34 may causecartilage and/or tissue to be scraped from the surface of at least oneof the ilium 14 and the sacrum 16. If it is desired to prepare a regionhaving a larger diameter, the cutting assembly 33 may be advancedfurther and then the undercutting system 10 may be rotated.

Depending on a variety of factors such as the sharpness of the cuttingassembly 33 and the hardness of the material being cut, it may not bepossible to merely cut through the cartilage and bone using just arotational motion. Rather, it may be necessary to alternate rotating theundercutting system 10 in clockwise and counter clockwise directions toincrease the area that is prepared.

The control knob can be periodically rotated to cause the cuttingassembly 33 to extend progressively further from the undercutting system10. While in many circumstances, it may be desirable to prepare acircular area, it is also possible to use the concepts of the inventionto prepare a portion of a circular area.

Alternatively or additionally, the probe assembly 32 may be withdrawnand a cutting assembly may be used to cut tissue in the region betweenthe ilium 14 and the sacrum 16 that has been defined by the probeassembly 32.

Contact between the cutting assembly 33 and the inner surfaces of theilium 14 and the sacrum 16 causes the respective surfaces to be abradedto create bleeding bone, which may be desirable to facilitate bonegrowth between the ilium 14 and the sacrum 16 as part of the sacroiliacfusion process.

A variety of techniques may be used to evaluate the amount of cartilagethat has been removed and the extent to which the surfaces of the iliumand the sacrum have been prepared. Examples of such suitable techniquesinclude monitoring the sound emitted during the cutting process, as thecutting of bone may make a scraping sound.

The person operating the undercutting system may monitor the performanceof the process using the feel of the cutting head, as it may be moredifficult for the cutting head to cut through the ilium and the sacrumthan the cartilage.

It is also possible to monitor the progress of the preparation for thesacroiliac fusion using a fluoroscope. While these techniques aredescribed individually, it is possible for one or more of the precedingtechniques to be combined.

In certain embodiments, the bits of cartilage and other tissue frombetween the ilium 14 and the sacrum 16 may become caught in the cuttingassembly 33 during the cutting process. In such a situation, thecartilage and other tissue are removed from between the ilium 14 and thesacrum 16 when the cutting assembly is retracted.

It may be necessary to clean the cutting assembly 33 and then reinsertthe cutting assembly 33 into the region between the ilium 14 and thesacrum 16 to remove additional bits of the cartilage and other tissue.

Alternatively or additionally, a technique may be utilized to remove thebits of cartilage and other tissue from between the ilium 14 and thesacrum 16. One suitable apparatus that may be used for remove the bitsof cartilage and other tissue is a radial deployment surgical tool,which is described in U.S. application Ser. No. 12/941,763, which wasfiled with the U.S. Patent & Trademark Office on Nov. 8, 2010, and whichis assigned to the assignee of the present patent application.

Another technique for removing the cut up bits of cartilage is to flushthe region with a fluid and then suction out the water with the cut upbits of cartilage. The process may be repeated until a desired amount ofthe cut up bits of cartilage is removed from between the ilium and thesacrum.

After the surfaces of the ilium and the sacrum have been prepared, abone graft may be inserted. Then, a variety of techniques may be used tomaintain the ilium and the sacrum in a fixed position with respect toeach other. Examples of suitable fixation techniques include bonescrews, cannulated screws, pins, cages, glue, coupled device with balland socket and Herbert screws.

Thereafter, bone screws 95 may be inserted into each of the apertures20, as illustrated in FIG. 13. The bone screws 95 will be effective atmaintaining the ilium 14 and the sacrum 16 in a stationary position withrespect to each other as bone grows between the ilium 14 and the sacrum16 to cause fusion of the ilium 14 and the sacrum 16.

In certain embodiments, the orientation of each of the apertures 20 maybe generally parallel to each other. In other embodiments, the apertures20 may be formed in a non-parallel relationship. In certain embodiments,in addition to the aperture that is prepared with the undercuttingsystem, one or more additional apertures may be formed on which theundercutting system is not used. These additional apertures may have asmaller diameter than the apertures in which the undercutting system isused.

For example, the two screws 95 on each side converge toward the safezone as illustrated in FIG. 13, which are lateral, inlet and outletfluoroscopic images of the pelvis region. It is to be noted that neitherof the bone screws 95 penetrate into the alar scope, which could becaused by the entry point being too cephalad. Such a situation is to beavoided because it can result in complications to the patient, whichrequires immediate correction.

While the figures only illustrated the procedure being performed on oneside of the patient, a person of skill in the art will appreciate thatthe process may be repeated on the other side of the patient.

While the concepts of the invention are primarily described inconjunction with preparation for a sacroiliac fusion, a person of skillin the art will appreciate that the concepts may be adapted for otherjoints in the body. The concepts may also be used for preparing aninterior region of a bone.

As an alternative to disturbing the surfaces of the ilium 14 and thesacrum 16 to expose bleeding bone, it is possible for the undercuttingsystem to remove more bone from at least one of the ilium 14 and thesacrum 16. Such a process could create a relatively planar preparedregion between the ilium 14 and the sacrum 16. Because the ilium 14 andthe sacrum 16 are not substantially flat, a greater amount of bone maybe removed using such a process. This process obliterates a portion ofat least one of the ilium 14 and the sacrum 16.

However, when performing such a process, care should be exercised sothat the cutting assembly does not cut all the way through the ilium 14or the sacrum 16. Additionally, care should be exercised to not removetoo much of the ilium 14 or the sacrum 16 as such a process could resultin weakening a portion of the ilium 14 or the sacrum 16 into which thefastening device is affixed.

The process associated with this embodiment may require the use of asharper and/or stronger cutting assembly 33 so that the cutting assembly33 resists damage when forces needed to cut more deeply into the ilium14 and sacrum 16 are used.

After the fusion region is prepared, the cut up bone, cartilage andother tissue may be removed from the fusion region using one of theprocesses described in the other portions of this patent application. Abone growth material may be placed into the fusion region. A bone screwor other fastening device may be used to retain the ilium 14 and thesacrum 16 in a stationary position with respect to each other while bonegrows between the ilium 14 and the sacrum 16.

An alternative embodiment of the undercutting system 110, which isillustrated in FIGS. 14-17, includes a cutting assembly 133 having aplurality of cutting elements 136 that are mounted with respect to asupport wire 138.

The cutting elements 136 include a central section 140 and two wingsections 142 on opposite sides of the central section 140. The centralsection 140 extends towards a distal end of the cutting assembly 133 andthe wing sections 142 extend toward the proximal end of the cuttingassembly 133.

The central section 140 has a width that is approximately the same as adistance between the wing section 142. When the cutting elements 136 areplaced in an adjacent relationship, the central section 140 extendsbetween the wing sections 142 on an adjacent cutting element 136.

This configuration causes the cutting elements 136 to resist lateralmovement with respect to each other as the undercutting system 110 isrotated. This configuration also reduces lateral pivoting of theadjacent cutting elements 136 with respect to each other.

In certain embodiments, a distal end 144 of the central section 140 on afirst cutting element 136 is adjacent to a proximal end 146 of thecentral section 140 on a second cutting element 136 that is adjacent tothe first cutting element 136. This configuration also reduces lateralpivoting of the adjacent cutting elements 136 with respect to eachother.

As illustrated in FIG. 17, the distal end 144 of the central section 140may be curved to facilitate vertical pivoting of the adjacent cuttingelements 136 with respect to each other. While not illustrated, it ispossible for the proximal end 146 of the central section 140 to also becurved.

The central section 140 has a height that is less than the height of thewing sections 142. The height of the central sections 140 may besubstantially the same on all of the cutting elements 136.

In certain embodiments, the two wing sections 142 on each cuttingelement 136 may be shaped substantially similar to each other. Each wingsection 142 has an upper surface 160 and a lower surface 162. The uppersurface 160 and the lower surface 162 may both be in a substantiallyhorizontal orientation. In other embodiments, the upper surface 160 andthe lower surface 162 may be oriented at an angle to enhance the abilityof the cutting elements 136 to cut through tissue and/or bone duringuse.

The wing sections 142 also include side surfaces 164 on the side of thewing section 142 that is opposite the central section 140. The sidesurfaces 164 may be in a generally vertical orientation. The wingsections 142 may each have a similar width so that when cutting elements136 are positioned adjacent to each other, the side surfaces 164 aregenerally aligned with each other.

The wing sections 142 each include a distal surface 170 and a proximalsurface 172. The distal surface 170 and the proximal surface 172 areeach oriented in a generally vertical orientation.

At least one of the distal surface 170 and the proximal surface 172 mayhave a convex configuration. In certain embodiments, one of the distalsurface 170 and the proximal surface 172 have a greater convexconfiguration.

An orientation of the convex configuration is between the upper surface160 and the lower surface 162 such that intermediate the upper surface160 and the lower surface 162, the cutting element 136 has the greatestwidth.

Each of the cutting elements 136 may have a similar smallest distancebetween the distal surface 170 and the proximal surface 172 and each ofthe cutting elements 136 may have a similar largest distance between thedistal surface 170 and the proximal surface 172.

Because of this configuration, an angle between the upper surface 160and the adjacent proximal surface 172 may be larger for the shortercutting elements 136 than for the taller cutting elements 136. Thisconfiguration provides the distal end of the cutting assembly 133 withenhanced flexibility compared to the proximal end of the cuttingassembly 133.

Using the convex configuration enhances the ability of adjacent cuttingelements 136 to vertically pivot with respect to each other such asmoving from a retracted configuration inside of the insertion apparatus130 to an extended configuration between the ilium 14 and the sacrum 16.The convex configuration also facilitates pivoting of the cuttingelements 136 with respect to each other when the cutting assembly 133 isrotated between the ilium 14 and the sacrum 16.

The wing sections 142 may be formed with different heights. Proximatethe distal end of the cutting assembly 133, the wing sections 142 mayhave a smaller height as compared to the height of the wing sections 142proximate the proximal end of the cutting assembly 133. Forming the wingsections 142 with the progressively larger height enables a greaterthickness of tissue between the ilium 14 and the sacrum 16 to beprepared.

The wing sections 142 proximate distal end of the cutting assembly 133may have a height of between about 2 millimeters and about 10millimeters. In certain embodiments, the wing sections 142 proximate thedistal end of the cutting assembly 133 have a height of about 4millimeters.

The wing sections 142 proximate the proximal end of the cutting assembly133 may have a height of between about 5 millimeters and about 15millimeters. In certain embodiments, the wing sections 142 proximate theproximal end of the cutting assembly 133 have a height of about 9millimeters.

On opposite sides of the central section 140, apertures 166 extendthrough each of the wing sections 142. The apertures 166 may begenerally cylindrical and have a diameter that is slightly larger thanthe diameter of the support wire 138. Alternatively or additionally, anaperture may be formed through each of the central sections 140 and suchapertures can receive the support wire 138.

The support wire 138 may be fabricated from a flexible material thatfacilitates repeated extension and retraction of the cutting assembly133. In certain embodiments, the support wire 138 is fabricated from ametallic material such as nitinol.

When the cutting elements 136 are assembled over the support wire 138,as illustrated in FIG. 16, the cutting elements 136 are substantiallyadjacent to each other but pivotable with respect to each other, asillustrated in FIG. 17.

A lock mechanism may be used to retain the cutting elements 136 in anadjacent relationship. The lock mechanism thereby enhances the abilityof the adjacent cutting elements 136 to impart force to each other.

The lock mechanism engages each end of the support wire 138 that extendsthrough the most proximal cutting element 136. The lock mechanism canreleasably engage the support wire 138. Such a configuration facilitatesreplacing the cutting elements 136 or the support wire 138 such as ifthe component is damaged.

As the undercutting system 10 rotates, the cutting assembly 133 can beconfigured to extend from the insertion apparatus 130. In certainembodiments, the rate at which the cutting assembly 133 extends from theinsertion apparatus 130 is selected so that one additional cuttingelement 136 is advanced for each rotation of the undercutting system 10.

Such a process produces a spiral cutting pattern, which is illustratedin FIG. 18. This process also facilitates cutting progressively deeperinto the tissue as the cutting assembly 133 is advanced from theinsertion apparatus 130.

The insertion apparatus 130 used in conjunction with this embodiment mayhave a similar configuration to the insertion apparatus 30 describedabove and illustrated in FIGS. 1-5. The insertion apparatus 130 mayinclude a curved channel 196 that directs the cutting assembly 133 froman orientation that is generally aligned with a central axis of theinsertion apparatus 30 to an orientation that is generally perpendicularto the central axis of the insertion apparatus 30.

In certain embodiments, the channel 196 may emerge from the insertionapparatus 130 on a lower surface of the insertion apparatus, asillustrated in FIG. 17. In such a configuration, the distal end of theinsertion apparatus 130 should be positioned in a spaced-apartconfiguration from the sacrum 16 to provide sufficient space between thesacrum and the distal end of the insertion apparatus to permit extensionof the cutting assembly 133 from the insertion apparatus 130.

The channel 196 may be formed with a profile that is similar to theprofile of the cutting elements 136 that includes a central channelsection and wing channel sections. The central channel section may beformed with a height and a width that are both slightly larger than theheight and the width, respectively, of the central section 140. The wingchannel sections are formed with a height and a width that are bothslightly larger than the height and the width, respectively, of thelargest wing section 142.

Forming the channel 196 with a size and shape that is similar to thesize and shape of the cutting elements 136 minimizes the potential ofthe cut tissue entering the interior of the undercutting system 110 andthereby potentially interfering with the operation of the undercuttingsy stem 110.

Another embodiment of the undercutting system 210, which is illustratedin FIGS. 19-22, utilizes a linear cutting motion, in contrast to therotational cutting motion utilized by the other configurations of theundercutting system that are described herein.

The cutting assembly 233 includes an elongated base 240 to which aplurality of cutting elements 242 are operably attached. The elongatedbase 240 may have a configuration that is similar to the probe assembly32 that is described with respect to the configuration illustrated inFIGS. 1-5.

The elongated base 240 may be fabricated from a flexible material suchas nitinol that enables the elongated base 240 to deflect from aretracted configuration inside of the insertion apparatus 230 in whichthe elongated base 240 is generally aligned with an axis of theinsertion apparatus 240. When in the extended configuration, at least adistal portion of the elongated base 240 may be oriented in a directionthat is generally perpendicular to the axis of the insertion apparatus240.

The elongated base 240 may be fabricated from a single layer or frommultiple layers. An advantage of fabricating the elongated base 240 frommultiple thinner layers is that the multiple thinner layers may be moreflexible than the thicker single layer.

A distal end of the elongated base 240 may be relatively thin to enhancethe ability of the distal end to form a path through tissue that isbetween the ilium 14 and the sacrum 16. However, the distal end of theelongated base 240 should not be too sharp to cause the distal end tocut into the ilium 14 or the sacrum 16 as the cutting assembly 233 isbeing extended from the insertion apparatus 230.

In certain embodiments, the distal end of the elongated base 240 isrounded between the upper and lower surfaces of the elongated base 240and is rounded between the opposite side surfaces of the elongated based240.

The cutting elements 242 are operably attached to at least one side ofthe elongated base 240. In certain embodiments, the cutting elements 242are attached to both sides of the elongated base 240. The cuttingelements 242 may be attached in an alternating configuration such everyother cutting element 242 is on an opposite side of the elongated base240.

The cutting elements 242 are movable with respect to the retractedconfiguration (FIGS. 19 and 21) and an extended configuration (FIGS. 20and 22). When the cutting elements 242 are in the retractedconfiguration, the cutting elements 242 are generally aligned with theupper and lower surfaces of the elongated base 240. The cutting elements242 are in the retracted configuration when the cutting assembly 233 isextended from the insertion apparatus 230.

To maximize the cutting capabilities of the undercutting system 210, thecutting elements 242 should be formed with a width that is as wide aspossible that can fit into the insertion apparatus 210. In certainembodiments, the cutting elements 242 have a width that is between about5 millimeters and about 10 millimeters.

The cutting elements 242 each comprise a distal end 250 and a proximalend 252. The proximal ends 252 of the cutting elements 242 are alloriented towards the distal end of the cutting assembly 233. Using thisconfiguration causes the cutting elements 242 to be in the retractedposition as the cutting assembly 233 is extended from the insertionapparatus 230. The cutting elements 242 pivot to the extended positionas the cutting assembly 233 is retracted into the insertion apparatus230.

The distal end 250 may be provided with a sharpened cutting surface tofacilitate the distal end 250 cutting through tissue between the ilium14 and the sacrum 16. The sharpened surface can also be sufficientlysharp to cut into the ilium 14 and the sacrum 16 and thereby facilitateproducing bleeding bone.

As an alternative to or in addition to sharpening the cutting elements242, an abrasive surface may be provided on at least a portion of theouter surface of the cutting elements 242. Examples of the abrasivesurface include chemical etching and sintering material such as beads onthe cutting elements 242. Alternatively or additionally, the cuttingelements 242 may have a plurality of bristles extending therefrom.Alternatively or additionally, a plurality of teeth may extend from oneof the surfaces of the elongated base 240 to provide the cutting action.

As an alternative to forming the cutting elements 242 separate from theelongated base 240, the cutting elements 242 may be integrally formedwith the elongated base 240. In this configuration, the cutting elements242 should have sufficient flexibility to move from the retractedposition to the extended position.

The proximal end 252 is used for operably attaching the cutting element242 to the elongated base 240. To reduce the overall thickness of thecutting assembly 233, the pivoting mechanism 244 may be mounted on aside of the elongated base 240 that is opposite the side on which thedistal end is located.

To maximize the cutting ability of the cutting assembly 233, theadjacent cutting elements 242 are mounted in an alternating relationshipon opposite sides of the elongated base 240. The distal end 250 of oneof the cutting elements 242 may be located proximate to the proximal end252 of the adjacent cutting element 242.

Because of the configuration in which the cutting elements 242 areattached to the elongated base 240, it is necessary for portions of eachcutting element 242 to be on both edges of the elongated base 240. Tominimize the potential of tissue snagging on the tissue on the portionsof the cutting elements 242 that extend between the opposite sides ofthe elongated base 240, notches may be formed along the edges of theelongated base 240. In certain embodiments, the cutting elements 242have a width that is not greater than the width of the elongated base240.

During the process of cutting tissue using this embodiment of theundercutting system, the cutting assembly 233 is extended and thenretracted to a position that is substantially within the insertionapparatus. It is not required that the cutting assembly 233 becompletely retracted into the insertion apparatus. Rather, a portion ofthe cutting assembly 233 that extends from the insertion apparatus doesnot interfere with the rotation of the undercutting system. Theundercutting system is rotated and the extension and retraction processis repeated.

A person of skill in the art will appreciate that the size of theprepared region can be increased by reducing the angle at which theundercutting system 210 is rotated between extensions. The desire toprepare a region having a larger area needs to be balanced with theadditional time that is needed for each of the extensions.

In certain embodiments, the cutting elements 242 each have a width ofabout 3.5 millimeters. In an undercutting process, the cutting assembly233 is extended between the ilium 14 and the sacrum 16 twelve timeswhere between each of the extensions, the undercutting system 210 isrotated about 30 degrees, as illustrated in FIG. 23.

Depending on factors such as the location of the aperture and the sizeof the patient, the cutting assembly 233 can be extended up to about 80millimeters. In other embodiments, the cutting assembly 233 is extendedabout 60 millimeters. Using this process enables an oblong regionbetween the ilium and the sacrum to be prepared, as illustrated in FIG.23.

In other embodiments, the cutting elements 242 each have a width ofabout 7.0 millimeters. In an undercutting process, the cutting assembly233 is extended between the ilium 14 and the sacrum 16 twelve timeswhere between each of the extensions, the undercutting system 210 isrotated about 30 degrees.

The length at which the cutting assembly 233 is extended can be selectedbased upon factors such as the distance of an edge of the ilium 14 andthe sacrum 16 from the aperture in the ilium 14. The distance that thecutting assembly 233 is extended should be greater than the diameter ofthe region that is desired to be prepared.

It is possible to monitor the distance in which the cutting assembly 236is extended using a component that is included in the undercuttingsystem 210. Alternatively or additionally, it is possible to monitor thedistance that the cutting assembly 236 has been extended using animaging technique such as fluoroscopy.

As an alternative to preparing the region between the ilium and sacrumfor fusion using a single aperture and extension of the cutting assemblyin different directions, as illustrated in FIG. 23, it is possible touse a second aperture. In this configuration, the cutting assembly isinserted through the first aperture in an orientation that is towardsthe second aperture.

Once the distal end of the cutting assembly is proximate the secondaperture, the distal end of the cutting assembly is retrieved throughthe second aperture. To facilitate guiding the cutting assembly from thefirst aperture to the second aperture, a probe may be provided on thedistal end of the cutting assembly. The probe may have a different shapeand/or size to facilitate efficiently directing the cutting assemblyfrom the first aperture to the second aperture.

A reciprocating motion can then be used to cut tissue that is locatedbetween the first aperture and the second aperture and between the iliumand the sacrum. Proximate the first aperture and the second aperture, aguide such as a roller may be provided to reduce the tendency of thecutting assembly to cut into the bone adjacent to the first aperture andthe second aperture as the cutting assembly transitions from anorientation that is generally transverse to the surface of the bone togenerally perpendicular to the surface of the bone.

During the cutting process, the insertion apparatus may be raised orlowered to facilitate preparing not only the region between the iliumand the sacrum but also to cause bleeding bone to be produced on atleast a portion of the ilium and the sacrum.

In another embodiment, the undercutting system 310 is rotated using apowered device 312, as illustrated in FIG. 24. In certain embodiments,the powered device 312 is a power drill. The power drill may be operableusing a variety of mechanisms. Examples of these power mechanismsinclude electricity, battery, pneumatic and hydraulic.

In this embodiment, the proximal end of the undercutting system 310includes an engagement mechanism that is used for operably attaching thepowered device 312 to the undercutting system 310. In certainembodiments, a first portion of the engagement mechanism 320 on theundercutting system 310 has a shape that is generally complementary to asecond portion of the engagement mechanism on the powered device 312. Incertain embodiments, the first portion 320 is an extension that has agenerally hexagonal shape and the second portion is a recess having agenerally hexagonal shape.

The first portion 320 may be operably attached to a proximal end of theprobe assembly 332 and/or a proximal end of the cutting assembly 333.Using such a configuration enables the probe assembly 332 and/or thecutting assembly 333 to rotate while enabling an outer shaft 340 toremain in a substantially stationary configuration with respect to thepatient during the rotation process.

The rotation of the undercutting system 310 may be done at a relativelyslow speed. Rotating the undercutting system 310 at a relatively slowspeed enhances the ability to control cutting of the ilium, the sacrumand the tissue between the ilium and the sacrum.

In certain embodiments, the rotation is at a speed of between about 15and about 120 revolutions per minute. In other embodiments, the rotationis at a speed of between about 15 and 30 revolutions per minute.

To enhance the ability to control the undercutting process, the outerportion of the undercutting system 310 may be held to retain the outerportion of the undercutting system 310 in a stationary configurationwith respect to the patient. In certain embodiments, a person maymanually hold the outer portion of the undercutting system 310. In otherembodiments, a handle 340 may be attached to the outer portion of theundercutting system 310 to thereby enhance the ability of the person tohold the outer portion of the undercutting system 310.

The handle 340 may be oriented substantially transverse to theorientation of the insertion apparatus. The handle 340 may have a lengththat is greater than the width of a typical user's hand. The handle 340may have a generally cylindrical shape with a diameter of between about½ of an inch and about 1 inch to facilitate the person's hand extendingaround the handle 340.

In certain embodiments, the rotation of the engagement mechanism 320relative to the handle 340 may cause the probe assembly 332 and/or thecutting assembly 333 to be deployed from the insertion apparatus 330.The rate of deployment may be between about 0.05 to about 0.25millimeters per revolution.

Control of the rotational rate may be done by varying the rate at whichthe power device 312 is rotated. Alternatively or additionally, theundercutting system 310 may include a gear assembly that enablesdifferent rotation rates to be obtained.

Rotation of the powered device 312 in a first direction causes the probeassembly 332 and/or the cutting assembly 333 to be extended from theinsertion apparatus 330. Rotation of the powered device 312 in a seconddirection, which is opposite the first direction, causes the probeassembly 332 and/or the cutting assembly 333 to the retracted into theinsertion apparatus 330.

The undercutting system 310 may also include a manual release mechanism342 that enables the probe assembly 332 and/or the cutting assembly 333to be manually retracted. While it is also possible for the manualrelease mechanism 342 to be used to manually extend the probe assembly332 and/or the cutting assembly 333, the manual extension of the probeassembly 332 and/or the cutting assembly 333 may not provide the samelevel of control as the use of the powered device 312.

In certain embodiments, brushes could be incorporate into the variousconfigurations of the cutting assemblies described herein. An advantageof using the brushes is that the brushes can cut tissue as well ascollect cut tissue to thereby facilitate removal of the cut tissue fromthe prepared region between the ilium and the sacrum.

Instead of or in addition to relying on flexibility of the probeassembly and/or the cutting assembly to track the joint between thesacrum and the ilium, it is possible to utilize a portion of theinsertion apparatus to guide the probe assembly and/or the cuttingassembly in a desired direction.

In such an embodiment, an angle at which the probe assembly and/or thecutting assembly is adjusted by changing a portion of the end cap at thedistal end of the insertion apparatus. In such a configuration, at leasta portion of the end cap is operably attached to the other portions ofthe insertion apparatus.

Using this configuration reduces the accuracy that must be used withselecting the location at which the aperture is to be drilled in theilium because in the other embodiments, it was desired for the locationof the aperture to be positioned and oriented substantiallyperpendicular to the adjacent surfaces of the sacrum and the ilium.

Additionally, using this configuration reduces the amount of bending ofthe probe assembly and/or the cutting assembly as these components exitfrom the insertion apparatus so that the probe assembly and/or thecutting assembly are generally aligned with the adjacent surfaces of theilium and the sacrum.

In one such configuration, the end cap 440 is operably attached to theinsertion apparatus 430 using a plurality of control arms 442, asillustrated in FIG. 25. A benefit of using this configuration is thatthe guide assembly and/or the cutting assembly will be more closelyaligned with the region between the ilium and the sacrum. As such, theguide assembly and/or the cutting assembly can be more rigid. Using thismore rigid configuration reduces the potential of damage to the guideassembly and/or the cutting assembly during the cutting process.

The control arms 442 may be positioned in a spaced-apart configurationproximate an outer surface of the insertion apparatus 430. In certainembodiments, a spacing between each of the control arms 442 isapproximately equal.

In one such configuration, there are four control arms 442 that operablyattach the end cap 440 to the insertion apparatus 430. Each of thecontrol arms 442 is mounted for movement with respect to the insertionapparatus 430. In certain embodiments, the control arms 442 are slidablewith respect to the insertion apparatus 430.

In other embodiments, at least a portion of each of the control arms 442has a threaded surface. Using the threaded surface enables rotation ofthe control arm 442 to cause the control arm 442 to move towards or awayfrom the distal end of the insertion apparatus 430 to thereby change theorientation of the end cap 440 with respect to the insertion apparatus430.

To facilitate pivoting of the end cap 440 with respect to the insertionapparatus 430 in all directions, the end cap 440 may be mounted in aspaced-apart configuration with respect to the distal end of theinsertion apparatus 430.

In certain embodiments, the end cap 440 can pivot with respect to theinsertion apparatus 430 between about 5 degrees and about 30 degrees. Inother embodiments, the end cap 440 can pivot at least about 20 degreeswith respect to the insertion apparatus 430.

In this configuration, the end cap 440 may include a plate portion 444and a cutter direction portion 446. The plate portion 444 may be usedfor operably attaching the end cap 440 to the control arms 442. In onesuch configuration, the plate portion 444 may have an aperture extendingtherethrough proximate to where the control arm 442 to be attached tothe plate portion 444.

The cutter direction portion 446 may be attached to the plate portion444 on a side thereof that is opposite the insertion apparatus 430. Anend of the cutter direction portion 446 that is opposite the plateportion 444 may be configured to extend into the sacrum. Using such aprocess may enhance the ability to retain the distal end of theundercutting system in a desired position during the undercuttingprocess.

In one configuration, the distal end of the cutter direction portion 446may be curved, as illustrated in FIG. 25. In another configuration, thedistal end of the cutter direction portion 446 may be pointed. Providingthe distal end of the cutter direction portion 446 with a pointedconfiguration may enhance the ability of the cutter direction portion446 to engage the sacrum.

The cutter direction portion 446 has a channel 450 that extendstherethrough similar to the embodiment illustrated in FIGS. 1-5. Thechannel 450 includes a proximal end that is generally aligned with acentral axis of the insertion apparatus.

The channel 450 includes a distal end that is oriented at an angle withrespect to the proximal end. In certain embodiments, the angle isbetween about 45 degrees and about 110 degrees. In other embodiments,the angle is between about 60 degrees and about 90 degrees.

Intermediate the proximal end and the distal end, the channel 450includes a transition region that causes the probe assembly 432 and/orthe cutting assembly 433 to deflect from the orientation at the proximalend to the orientation at the distal end.

While it is illustrated that the distal end of the channel 450 extendsthrough a side surface of the cutter direction portion, it is possiblefor the distal end of the channel 450 to extend through a lower surfaceof the cutter direction portion 446 or to extend through both the sidesurface and the lower surface of the cutter direction portion 446.

The distal end of each control arm 442 may be attached to the end cap440 using a variety of mechanisms that facilitate retaining the controlarm 442 in engagement with the end cap 440 while permitting the end cap440 to pivot with respect to the end cap. An example of one suitablemechanism for attaching the control arm 442 to the end cap 440 is ascrew. In certain embodiments, the screw may be recessed in the end cap440.

Sliding or rotation of the control arms 442 may be controlled using acontrol mechanism that is mounted proximate the proximal end of theinsertion apparatus 430. Providing the control mechanism proximate theproximal end of the insertion apparatus 430 minimizes the size of theincision that needs to be made in the patient and the aperture thatneeds to be drilled in the bone to provide access to the region betweenthe bones that is to be prepared with the undercutting system.

In certain embodiments, the control mechanism facilitates manual pushingor pulling of the control arms 442. Each of the control arms 442 mayinclude a configuration proximate a proximal end thereof to facilitategripping by a person desiring to change the position of the control arm442. In one such configuration, a handle is provides on each of thecontrol arms 442.

Alternatively or additionally, a mechanical assist may be used tocontrol movement of the control arms 442. An example of one suchmechanical assist is a servo motor. Other possible configurations forthe mechanical assist include pneumatic and hydraulic.

In another embodiment, three control arms 442 operably attach the endcap 440 to the insertion apparatus 430. The control arms 442 may bemounted in a spaced-apart configuration so that a spacing betweenadjacent control arms 442 is approximately equal.

In another embodiment, a hinge mechanism is provided along a first edgeof the end cap to pivotally attach the end cap to the hinge mechanism.An edge of the end cap that is opposite the hinge mechanism is operablyattached to at least one control arm. Similar to the control armsdiscussed above, the control arm causes the end cap to pivot withrespect to the insertion apparatus.

Operably attaching the end cap to the insertion apparatus using thecontrol arms enables a direction at which the probe assembly and/or thecutting assembly extends from the undercutting system to be in adirection that generally conforms to an orientation of the surfaces ofthe ilium and the sacrum.

As such, an element associated with using this configuration of theundercutting system utilizes imaging to assist in setting theorientation of the end cap 440. In one such configuration, a fluoroscopeis used for at least one orientation to evaluate the orientation of theilium and the sacrum proximate to where the undercutting system is to beused.

In another configuration, the end cap 540 is movably mounted withrespect to the distal end of the insertion apparatus 530, as illustratedin FIGS. 26 and 27. In this configuration a flexible material is used tooperably mount the end cap 540 with respect to the insertion apparatus530.

Using this configuration allows the end cap 540 to pivot with respect tothe insertion apparatus 530 during the process of using the probeassembly and/or the cutting assembly to prepare the region between theilium and the sacrum for the sacroiliac fusion. By pivoting the end cap540, the bending of the portion of the probe assembly and/or the cuttingassembly that extends beyond the end cap 540 is reduced.

A distance between the insertion apparatus 530 and the end cap 540 mayaffect the angle at which the end cap 540 is pivotable with respect tothe insertion apparatus 530. Similarly, the resilient material that isused to operably attach the end cap 540 to the insertion apparatus 530can also affect not only the angle at which the end cap 540 is pivotablewith respect to the insertion apparatus 530 but also the ease at whichthe end cap 540 pivots with respect to the insertion apparatus 530.

As an alternative to using the resilient material to attach the end cap540 to the insertion apparatus, it is possible to use other mechanisms.An example of one such alternative attachment mechanism is a hinge.

The end cap 540 includes a channel 550 extending therethrough thatcauses the probe assembly and/or the cutting assembly to be deflectedfrom an initial configuration that is generally parallel to the axis ofthe insertion apparatus 530 to a configuration that is generallyperpendicular to the axis of the insertion apparatus 530 as the probeassembly and/or the cutting assembly emerges from the end cap 540.

The channel 550 may be formed with a width and a height that are bothgreater than the width and the height of the probe assembly and thecutting assembly. Using such a configuration enables the end cap 540 topivot with respect to the insertion apparatus 530 without the contact ofthe probe assembly or cutting assembly against the side of the channel550 restricting the pivoting of the end cap 540.

Another configuration of the undercutting system enables pivoting of theend cap 640 with respect to the insertion apparatus 630, as illustratedin FIGS. 28 and 29. At least a portion 660 of the distal end of theinsertion apparatus 630 may have a semi-circular configuration toenhance the ability of the end cap 640 to pivot with respect to theinsertion apparatus 630.

The end cap 640 may have a recess 662 formed therein that is adapted toreceive the portion 660 of the distal end of the insertion apparatus630. At least part of the recess 662 may have a semi-circularconfiguration to enhance the ability of the end cap 640 the pivot withrespect to the insertion apparatus 630.

The channel 650 extends through the distal end of the insertionapparatus 630. The channel 650 may be formed with a height and a widththat are both greater than the height and the width of the probeassembly and the cutting assembly to facilitate pivoting of the end cap640 with respect to the insertion apparatus 630. Similarly, the channel650 in the end cap 640 may also be formed with greater dimensions tofacilitate pivoting of the end cap 640 with respect to the insertionapparatus 630.

A retaining pin 670 may be used to prevent the end cap 640 from becomingdisengaged from the insertion apparatus 630. The retaining pin 670 mayextend across the end cap 640 as illustrated in FIG. 28. A groove 672may be formed in the insertion apparatus 630 proximate the distal endthereof. The groove 672 may extend substantially around the outersurface of the insertion apparatus 630. The groove 672 receives theretaining pin 670 to thereby retain the end cap 640 in pivotalengagement with the insertion apparatus 630.

A few of the challenges associated with preparing bleeding bone surfaceson the ilium and the sacrum include providing the probe assembly and/orthe cutting assembly that is deflectable from an initial configurationinside of the insertion apparatus to an extended configuration betweenthe ilium and the sacrum while at the same time the probe assemblyand/or the cutting assembly have sufficient structural rigidity to cutthrough tissue between the ilium and the sacrum as the probe assemblyand/or the cutting assembly is progressively extended from the insertionapparatus into the space between the ilium and the sacrum so that aprogressively larger area can be prepared.

Additional challenges associated with preparing the bleeding bonesurfaces on the ilium and the sacrum result from the fact that thesurfaces of the ilium and the sacrum are not substantially flat and adistance between the ilium and the sacrum does not remain consistent.

Another embodiment of the cutting assembly, which is illustrated inFIGS. 30-33, seeks to overcome these issues. The cutting assembly 733includes an outer cutting portion 740 and an inner expansion portion742.

The outer cutting portion 740 includes a relatively thin distal end 750.While the distal end 750 may have a thickness that is less than thethickness of the other portions of the cutting assembly 733, it does nothave to be very sharp. Such a configuration facilitate defining thejoint line between the ilium and the sacrum as the cutting assembly 733is extended from the insertion apparatus while minimizing the cuttingassembly 733 cutting too deeply into the ilium or the sacrum.

Cutting too deeply into the ilium or the sacrum is undesirable becausethe ilium and the sacrum are considerably harder than the tissue that isbetween the ilium and the sacrum. Greater force is thereby needed to cutinto the ilium or the sacrum than is needed to cut the tissue betweenthe ilium and the sacrum.

Such additional force requires the components of the undercutting systemto be stronger than if the undercutting system is intended to cutthrough the tissue between the ilium and the sacrum as well as todisturb the surfaces of the ilium and the sacrum to produce bleedingbone. The additional force needed to cut through the ilium or the sacrumalso presents challenges in providing such force through the insertionapparatus, which has a relatively thin diameter.

The outer cutting portion 740 may include an upper cutting portion legand a lower cutting portion leg. Each of the cutting portion legs mayinclude a flexible base 754 to which a plurality of cutting elements 752is mounted.

The flexible base 754 enables the outer cutting portion 740 to deformfrom the initial configuration (FIG. 30) to the expanded configuration(FIG. 33). A variety of materials may be used to fabricate the flexiblebase 754 as long as such materials are suited for use in medicalapplications.

The cutting elements 752 include a sharpened surface along at least oneside edge thereof. In certain embodiments, the sharpened surfaces areprovided on both side edges of each cutting element 752 so that thecutting assembly 733 is capable of cutting tissues when rotated in bothdirections.

In other embodiments, one of the side edges has a sharper surface andthe opposite side edge. In certain embodiments, the cutting elements 752are fabricated from a metallic material such as stainless steel, whichis suited for use in medical applications.

In still other embodiments, the cutting elements 752 may include anabrasive outer surface. This abrasive outer surface may be in additionto or as an alternative to the sharpened surfaces. Alternatively oradditionally, the cutting elements 752 may have a plurality of bristlesextending therefrom.

The inner expansion portion 742 is positioned between the upper cuttingportion leg and the lower cutting portion leg. In certain embodiments,the inner expansion portion 742 extends substantially to the distal endof the cutting assembly 733.

The inner expansion portion 742 may be formed with a width that is lessthan the width of the outer cutting portion 740. In other embodiments,the inner expansion portion 742 has a width that is approximately thesame as the width of the outer cutting portion 740.

The inner expansion portion 742 may be fabricated from a flexiblematerial. A person of skill in the art will appreciate that the flexiblematerial needs to be sufficiently strong to cause the inner expansionportion 742 to expand from the retracted position to the expandedposition while resisting damage from contact with the outer cuttingportion 740 as well as contact with the ilium, the sacrum and the tissuethat is between the ilium and the sacrum. In certain embodiments, theinner expansion portion 742 is fabricated from a polymeric material.

The inner expansion portion 742 may be moved between the retractedposition and the expanded position by placing an object therein. Onecriteria in selecting the material that is placed in the inner expansionportion 742 is the ability to readily insert and remove the object fromthe inner expansion portion 742.

In certain embodiments, the object placed in the inner expansion portion742 is a gas such as air. In other embodiments, the object placed in theinner expansion portion 742 is a liquid such as water. In still otherembodiments, the object placed in the inner expansion portion 742 is asolid such as beads. In other embodiments, the object placed in theinner expansion portion is a series of strips that are inserted in asequential manner to gradually increase the thickness. In a situation,where the object is the series of strips, it may not be necessary forthe inner expansion portion 742 to be used.

While it is intended that the object placed in the inner expansionportion 742 is to remain inside of the inner expansion portion 742 andnot contact the patient, it is possible that the object may contact thepatient. Accordingly, the object should be selected to not cause anynegative interactions if the object comes into contact with either theskin on the surface of the patient or tissue inside of the patientproximate to where the undercutting system is being used.

When the cutting assembly 733 is in the insertion apparatus and theninitially extended from the insertion apparatus, the inner expansionportion 742 is in a relatively flat configuration, as illustrated inFIG. 30.

Thereafter, the inner expansion portion 742 is progressively increasedin size as illustrated in FIGS. 31-33. This process enables aprogressively thicker region to be prepared between the ilium and thesacrum.

In certain embodiments, the increasing the size of the inner expansionportion 742 is gradually done as the cutting assembly 733 is rotated. Inother embodiments, the inner expansion portion 742 is periodicallyincreased in size such as after each rotation of the cutting assembly733.

Initially, the outer cutting portion 740 cuts the tissue between theilium and the sacrum. The flexible nature of the outer cutting portion740 and the inner expansion portion 742 facilitates the cutting assemblyfollowing the surfaces of the ilium and the sacrum as well asaccommodates for differences in the distance between the ilium and thesacrum.

Once the inner expansion portion 742 is in the expanded position, whichis illustrated in FIG. 33, the upper cutting portion leg and the lowercutting portion leg are sufficiently urged against the surfaces of theilium and the sacrum to disrupt such surfaces and cause bleeding bone onthese surfaces. As described above, the bleeding bone is an importantaspect in providing sacroiliac fusion.

After the cutting process is complete, the object is removed from theinner expansion portion 742 so that the outer cutting portion 740 mayreturn to the initial collapsed configuration where the upper cuttingportion leg is proximate the lower cutting portion leg as illustrated inFIG. 30. At such time, the cutting assembly 733 is withdrawn frombetween the ilium and the sacrum.

While the concepts of the invention are primarily described inconjunction with preparation for a sacroiliac fusion, a person of skillin the art will appreciate that the concepts may be adapted for otherjoints in the body. The concepts may also be used for preparing aninterior region of a bone.

In the preceding detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting.

It is to be understood that other embodiments may be utilized andstructural or logical changes may be made without departing from thescope of the present invention. The preceding detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims.

It is contemplated that features disclosed in this application, as wellas those described in the above applications incorporated by reference,can be mixed and matched to suit particular circumstances. Various othermodifications and changes will be apparent to those of ordinary skill.

1. A tool for cutting tissue, comprising: an elongate outer shaft havingan outer sidewall extending between proximal and distal ends of theelongate outer shaft; a cutting assembly having an elongate cuttingmember, the elongate cutting member having proximal and distal ends anda longitudinal axis extending between the proximal and distal ends; anarticulated portion of the elongate cutting member configured to allowthe distal end of the elongate cutting member to be shifted in adirection transverse to the longitudinal axis; and a cutting element ofthe elongate cutting member configured for cutting or abrading tissue;wherein the elongate cutting member is configured for being shiftedbetween a retracted position, wherein the elongate cutting memberincluding the cutting element is disposed completely within the elongateouter shaft, and an extended position, wherein the articulated portionof the elongate cutting member is shifted in the direction transverse tothe longitudinal axis such that the distal end and the cutting elementof the elongate cutting member extend laterally beyond the outersidewall of the elongate outer shaft to allow the cutting element to cutor abrade tissue located laterally to the outer sidewall of the elongateouter shaft.
 2. The tool of claim 1, wherein the elongate cutting memberhas a body with an outer periphery, and wherein the cutting elementextends beyond the outer periphery of a portion of the body locatedproximally of the cutting element.
 3. The tool of claim 1, wherein atleast a part of the articulated portion of the elongate cutting memberextends laterally beyond the outer sidewall of the elongate outer shaftwhen the elongate cutting member is in the extended position.
 4. Thetool of claim 1, wherein at least a part of the articulated portion ofthe elongate cutting member is configured for cutting or abrading tissuelocated laterally to the outer sidewall of the elongate outer shaft. 5.The tool of claim 1, further comprising a guide channel at the distalend of the elongate outer shaft for guiding at least the distal end ofthe elongate cutting member therethrough, wherein the guide channelincludes an arcuate portion for directing the distal end of the elongatecutting member in the direction transverse to the longitudinal axis. 6.The tool of claim 5, further comprising an end cap mounted to the distalend of the elongate outer shaft, wherein the guide channel is disposedin the end cap.
 7. The tool of claim 1, wherein the elongate cuttingmember includes at least a top and a bottom side, and the cuttingelement is disposed on the top side, and wherein the top side of theelongate cutting member adjacent the cutting element faces proximallywhen the cutting element is in the extended position.
 8. The tool ofclaim 1, wherein the elongate cutting member has a tubular body with athroughopening extending between the proximal and distal ends thereof.9. The tool of claim 1, wherein the articulated portion of elongatecutting member includes a plurality of kerfs or notches.
 10. The tool ofclaim 9, wherein the elongate cutting member is formed by an elongateshaft and the articulated portion of the elongate cutting memberincludes a plurality of segments spaced by the kerfs or notches alongthe shaft, whereby the articulated portion is a segmented articulatedportion.
 11. The tool of claim 9, wherein the elongate cutting memberincludes at least a top and a bottom side, wherein the plurality ofkerfs or notches are formed in the top side of the elongate cuttingmember.
 12. The tool of claim 9, wherein the plurality of kerfs ornotches are formed in the elongate cutting member adjacent to the distalend thereof.
 13. The tool of claim 1, further comprising an elongateprobe member having proximal and distal ends, wherein the elongate probemember is configured for being shifted between a retracted position,wherein the elongate probe member is disposed completely within theelongate outer shaft, and an extended position, wherein at least thedistal end of the elongate probe member extends laterally beyond theouter sidewall of the elongate outer shaft.
 14. The tool of claim 13,wherein the elongate cutting member has a tubular body with athroughopening extending between the proximal and distal ends thereof,and wherein the elongate probe member is disposed at least partiallywithin the throughopening of the elongate cutting member when theelongate cutting member and the elongate probe member are in theirrespective retracted positions.
 15. The tool of claim 13, wherein theelongate probe member is formed of a nitinol material.
 16. The tool ofclaim 13, wherein the elongate probe member is formed by two elongatestrip members in engagement with one another.
 17. The tool of claim 16,wherein each of the two elongate strip members has a thickness, and thethickness of one of the elongate strip members is greater than thethickness of the other elongate strip member.
 18. The tool of claim 13,wherein the elongate probe member is connected to the elongate cuttingmember such that shifting the elongate cutting member from the retractedposition to the extended position thereof causes the elongate probemember to shift from the retracted position to the extended positionthereof.
 19. The tool of claim 13, wherein in their respective extendedpositions, the distal end of the elongate probe member extends laterallyfurther beyond the outer sidewall of the elongate outer shaft than thedistal end of the elongate cutting member.
 20. The tool of claim 13,wherein the elongate probe member is connected to the elongate cuttingmember closer to the proximal end of the elongate cutting member thanthe distal end thereof.
 21. The tool of claim 13, further comprising anactuator operably connected to the elongate cutting member and theelongate probe member, wherein the actuator is operable to shift theelongate cutting member and the elongate probe member between theirrespective retracted and extended positions.
 22. The tool of claim 21,wherein the actuator is operable to simultaneously shift the elongatecutting member and the elongate probe member from their respectiveretracted positions to their respective extended positions, and theactuator is operable to simultaneously shift the elongate cutting memberand the elongate probe member from their respective extended positionsto their respective retracted positions.
 23. The tool of claim 21,wherein the actuator is a rotatable knob, wherein rotating the rotatableknob in a first direction causes the elongate cutting member to movefrom the retracted position to the extended position, and rotating therotatable knob in a second direction causes the elongate cutting memberin the extended position to shift to the retracted position.
 24. Thetool of claim 23, further comprising a drive shaft having a longitudinalaxis, wherein the drive shaft is disposed within the elongate outershaft and is operably connected to the elongate cutting member and therotatable knob for shifting the elongate cutting member between itsretracted and extended positions, wherein rotating the rotatable knob inone direction causes the drive shaft to shift proximally along itslongitudinal axis for retracting the elongate cutting member, androtating the rotatable knob in another direction causes the drive shaftto shift distally along its longitudinal axis for extending the elongatecutting member.